Arnon Lotem
Publications with abstracts Return to my home page
Shafir S, Reich T, Tsur E, Erev I, and Lotem A.
2008.
Perceptual accuracy and conflicting effects of certainty on
risk-taking behaviour. Nature 453:
917-920 Full
Text | PDF
(221K) See also: Making
the paper: Arnon Lotem Nature podcast: interview with Ido Erev media coverage
Abstract: The 'certainty effect'1,
2
is a notable violation of expected utility theory by decision makers3,
4,
5,
6.
It shows that people's tendency to select the safer of two prospects increases
when this prospect provides a good outcome with certainty (for example, people
prefer a monetary gain of 3 with certainty over 4 with a probability of 0.8,
but do not prefer 3 with a probability of 0.25 over 4 with a probability of
0.2). Subsequent work on experience-based decision making in rats7
extended the certainty effect to other animals, suggesting its generality
across different species and different decision-making mechanisms. However, an
attempt to replicate this study with human subjects showed a surprising
'reversed certainty effect'8,
9,
namely, the tendency to prefer the safer option decreases when this prospect is
associated with certainty (and people now prefer 4 with a probability of 0.8
over 3 with certainty). Here we show that these conflicting results can be
explained by perceptual noise and that the certainty effect can be restored
experimentally by reducing perceptual accuracy. Using complementary experiments
in humans and honeybees (Apis mellifera), we show that by manipulating perceptual
accuracy in experience-based tasks, both the certainty and the reversed
certainty effects can be exhibited by humans and other animals: the certainty
effect emerges when it is difficult to discriminate between the different
rewards, whereas the reversed certainty effect emerges when discrimination is
easy. Our results fit a simple process-based model of matching behaviour10,
11,
capable of explaining the certainty effect in humans and other animals that
make repeated decisions based on experience. This mechanism should probably be
distinguished from those involved in the original certainty effect that was
exhibited by human subjects in single description-based problems1,
2.
Lotem A. and Halpern J.Y.
Abstract: A data-driven model of
learning is proposed, where a network of nodes and links is constructed that
represents what has been heard and observed. Autism is viewed as the
consequence of a disorder in the data-acquisition component of the
model---essentially, it is the result of getting an ``inappropriate''
distribution of data. The inappropriate data distribution leads to problems in
data segmentation, which, in turn leads to a poor network representation. It is
shown how the model, given inappropriate data distributions, can reproduce the
main cognitive deficits associated with autism, including weak central
coherence, impaired theory of mind, and executive dysfunction. In addition, it
is shown how the model itself can explain the inappropriate data distribution
as the result of an inappropriate initial network. Finally, we discuss the
relationships between our model and existing neurological models of autism, and
the possible implications of our model for treatment.
Uri Grodzinski,
Ido Erev, and Arnon Lotem 2008. Can hungry nestlings
be trained to reduce their begging? Behavioral Ecology 19:
116-125 PDF
Abstract: Nestling begging
behavior is usually characterized by a behavioral response of increasing
begging levels with an increase in nestling need or hunger. Recent evidence for
the possible effect of learning on begging intensity raises the question of how
learning can shape this response rule. In particular, it is not clear whether
hungry nestlings can learn to reduce their begging when it is not successful
or, rather, whether they must first acquire positive experiences with low
begging levels in order to do so. To explore this question, we conducted 3
hand-feeding experiments with pairs of house sparrow (Passer domesticus) nestlings. In the first 2 experiments, the
nestlings targeted to lower their begging were rewarded mainly or only for low
begging postures. However, despite the high expected reward for low begging,
these nestlings did not lower their begging. Controlled by their behavioral
response function, hungry nestlings were "stuck" at high postures
without being able to experience the potential success of low postures. In the
third experiment, nestlings targeted to lower their begging levels were
rewarded for any begging posture, ensuring that satiation would provide their
initial "positive experience" with low begging postures. Begging
postures were reduced by this treatment. In light of these results, we suggest
that parents are unlikely to reduce offspring begging levels by simply ignoring
them. However, they might be able to do so by attending to the begging as soon
as possible, thereby allowing their offspring to explore low begging and learn
that it is sufficiently effective.
Katsnelson
E, Motro U, Feldman MW, and Lotem A. 2008. Early experience
affects producer–scrounger foraging tendencies in the house sparrow. Animal
Behaviour, In press.
(Available online November 19, 2007) PDF
Abstract: Group foragers can
use a ‘producer’ tactic which involves searching for food or a ‘scrounger’
tactic which involves joining others who have discovered food. While these
alternative behaviours are well documented, it is not
clear to what extent an individual's tendency to forage independently or to
follow others is under genetic control or rather is affected by experience. To
examine whether hand-reared juveniles can learn to prefer using a producer or a
scrounger tactic, we hand-reared house sparrow, Passer domesticus,
nestlings that upon fledging were assigned to one of two training groups; the
first was expected to enhance joining (scrounging) behaviour
and the second to enhance searching (producing) behaviour.
In the first group, fledglings were imprinted on a parent model (stuffed female
sparrow) that visited locations containing food. In the second group,
fledglings were imprinted on a parent model that visited locations containing
no food, while food was available in different locations. At the end of a 5-day
training phase, all fledglings were released into a shared aviary, and their
social foraging tendencies were measured. We found that fledglings from the
first group used significantly more joining behaviour
than fledglings from the second group, suggesting that an individual whose
early experience positively reinforced joining behaviour
is more likely to later become a joiner. To our knowledge, this is the first
experimental evidence for the effect of learning on the choice between social
foraging strategies in the context of the producer–scrounger game.
Adar E, Lotem A. and
A. Barnea 2008. The
effect of social environment on singing behavior in the zebra finch (Taeniopygia guttata) and its
implication for neuronal recruitment. Behavioural
Brain Research 187: 178-84 (Available online 17 September 2007) PDF
Abstract: Previous studies
found that complex social environment increases new neuronal recruitment in
brains of adult male zebra finches, in comparison with exposure to a simple
social environment. These experiments could not determine, however, whether
this increase was due to greater amounts of auditory input (amount of auditory
information the male is exposed to), or auditory output (amount of song it
produces). To answer this question, we raised male zebra finches to adulthood
in a controlled environment, and were then exposed them to either a single
unfamiliar female (simple social environment) or to 45 unfamiliar zebra finches
of both sexes (complex social environment). Their singing behavior was
monitored in these new social environments. Birds which were exposed to a
simple social environment sang significantly more than birds which were exposed
to a complex social environment. This supports the hypothesis that increased
neuronal recruitment in birds exposed to a complex social environment
correlates with processing and storing of auditory input, and not with song
produced by the bird.
Grodzinski U, Lotem A. 2007. The adaptive value of parental responsiveness to nestling begging.
Proceedings of the Royal Society of
Abstract: Despite extensive
theoretical and empirical research into offspring food solicitation behaviour as a model for parent–offspring conflict and
communication, the adaptive value of parental responsiveness to begging has
never been tested experimentally. Game theory models, as well as empirical
studies, suggest that begging conveys information on offspring state, which
implies that parental investment can be better translated to fitness by
responding to begging when allocating resources rather than by ignoring it.
However, this assumption and its underlying mechanisms have received little or
no attention. Here we show by experiments with hand-raised house sparrow
(Passer domesticus) nestlings that a ‘responsive
parent’ will do better than a hypothetical ‘non-responsive’ mutant (that
provides similar food amounts, but irrespective of begging). This is neither
because food-deprived nestlings convert food to mass more efficiently, however,
nor because responsiveness reduces costly begging. Rather, responsiveness to
begging is adaptive because it reduces two opposing risks: one is wasting time
when returning too soon to feed already satiated nestlings and the other is
repeatedly overlooking some nestlings as a result of the stochastic nature of a
random, non-responsive strategy. This study provides the first experimental
evidence for the adaptive value of parental responsiveness to offspring
begging.
Dor R., Kedar H., Winkler WD. & Lotem 2007. Begging
in the absence of parents: a "quick on the trigger" strategy to
minimize costly misses. Behavioral Ecology, 18: 97-102 PDF
Abstract: Nestling begging in
the absence of parents may reflect ‘‘false alarms’’ due to cognitive
constraints or signaling activity toward nest mates (sibling
negotiation).According to signal detection theory, cognitive constraints should
result in both false alarms (begging in the absence of parents or to
inappropriate stimuli)and misses (failure to beg during parental visits).In our
study of house sparrows, nestling begging in the absence of parents comprised
up to 50%of the begging events at the nest and was more frequent at an early
age and among hungrier (lower ranked)nestlings. In contrast, the probability of
begging during parental visits was constantly high (80%or more), suggesting
that the rate of misses must have been low even at an early age. These results
have 2 main implications. First, the observation that begging
in the absence of parents decreases with nestling age favors the cognitive
constraints hypothesis over functional explanations such as the sibling
negotiation hypothesis. Second, the low proportion of ‘‘misses’’ among
young nestlings suggests that nestling respond to their cognitive constraints
by using low decision criteria (a ‘‘quick on the trigger’’ strategy) that
increases the frequency of false alarms but minimizes costly misses.
Munichor
N.,
Abstract: Four experiments are presented that explore
situations in which a decision maker has to rely on personal experience in an
attempt to minimize delays. Experiment 1 shows that risk-attitude in these
timesaving decisions is similar to risk-attitude in money-related decisions
from experience: A risky prospect is more attractive than a safer prospect with
the same expected value only when it leads to a better outcome most of the
time. Experiment 2 highlights a boundary condition: It suggests that a
difficulty in ranking the relevant delays moves behavior toward random choice.
Experiments 3 and 4 show that when actions must be taken during the delay
(thereby helping compare delays),this increases the
similarity of timesaving decisions to money-related decisions. In these
settings the results reflect an increase in risk aversion with experience. The
relationship of the results to the study of non-human time-related decisions,
human money-related decisions and human time perception is discussed.
Abstract: In lekking species females visit male aggregations solely to copulate or have their eggs fertilized. Because lekking males do not contribute to parental care, evolutionary theory does not expect them to be choosy. However, we show here that in the cichlid fish Astatotilapia flaviijosephi the lekking males exhibit sequential mate preference that strongly suggests a trade-off between present and future reproductive effort. We tested mate preferences of A. flaviijosephi males by sequentially presenting them with two images of a gravid female, differing only in size. Previously, males were shown to prefer larger, more fecund females in simultaneous preference tests. The sequential presentation experiment reported here indicates that even in the absence of simultaneous presentation, males spent more time courting larger female images, and stayed longer in their vicinity. Thus, our study suggests that lekking males may be much choosier than previously appreciated. Furthermore, considering the intense competition among lekking males we also suggest that male choosiness, combined with other factors, may help to solve the 'paradox of the lek'. It can make less attractive females more available to subordinate males, thereby increasing the contribution of the latter to the population gene pool and keeping genetic variability among males at a level that justifies female choice.
Ben-Dov A., Vortman Y. & Lotem A. 2006. First documentation of sibling cannibalism in a small passerine species. Ibis 148: 365-367. PDF
No abstract. In this paper, we report on a female House Sparrow, Passer domesticus, caught on video camera feeding her nestlings with the carcass of their dead sibling. See video clip at: http://www.tau.ac.il/video/Research/Life_Sciences/Zoology/Animal_Behavior/cannibalism_in_sparrows/
Lotem A. & Winkler DW. 2005 Defining the Concept of Public Information. Science 308: 354. PDF (no abstract)
Lotem A. & Winkler DW. Can reinforcement learning explain variation in early infant crying? Behavioral and Brain Sciences 27: 468. (PDF version)
Abstract: We welcome Soltis' use of evolutionary signaling theory, but question his interpretations of colic as a signal of vigor and his explanation of abnormal high-pitched crying as a signal of poor quality. Instead, we suggest that these phenomena may be sub-optimal by-products of a generally adaptive learning process by which infants adjust their crying levels in relation to parental responsiveness.
Werner N.Y., Balshine-Earn S., Leach
B. & Lotem A. Helping opportunities and space segregation among helpers in
co-operatively breeding cichlid. Behavioral Ecology 14:749–756. (PDF
version)
Abstract: Studies of cooperative breeding have largely ignored
the role of conflict among helpers and how it shapes group dynamics and helping
behavior. In this study, using laboratory experiments with cooperatively
breeding cichlids from
Fishman MA, Stone L & Lotem A. 2003
Fertility assurance through extrapair
paternity, and male paternity defense. J. Theor.
Biol. 221:96-107. (PDF
version)
Abstract: Extrapair paternity has been
observed in many formally monogamous species. Male pursuit of extrapair fertilizations is explained by the advantages of
having offspring that receive essential paternal care from other males. Since
females are capable of exercising a degree of control over the post copulatory sperm competition, extrapair
paternity cannot persist unless it confers fitness benefits on cuckolding
females. Thus, extrapair paternity involves
cooperation between mated females and extrapair
males. On the other hand, paired males frequently exhibit strategies that
minimize their loss of paternity and/or conserve paternal investment if
paternity is lost. Hence, extrapair attributes of
diverse species and populations reported in the literature are particular
solutions of evolutionary games involving gender-specific
cuckolding/anti-cuckolding strategies. Here we use methods of evolutionary game
theory to study the role of male paternity guarding strategies in situations
where females seek extrapair fertilizations for reasons
of genetic compatibility and/or in pursuit of genetic diversity for their
offspring. Our results indicate that in these circumstances pursuit of extrapair fertilizations is the only evolutionary stable
female strategy. Males, on the other hand, have two, mutually exclusive,
evolutionary stable strategies: full time pursuit of extrapair
fertilizations and a compromise strategy wherein they protect in-pair paternity
during their mate’s fertile periods and pursue extrapair
paternity the rest of the time. The relative merits of these two strategies are
determined by the efficiency of male in-pair paternity defense, breeding
synchrony, fitness advantages of extrapair over
in-pair offspring, and the intensity of competition for extrapair
fertilizations from floater males.
Abstract: Current theories of mate choice predict that the level
of choosiness exhibited by the different sexes will depend on their relative
investment in parental care. Females often invest more than males (both in the
pre- and post-zygotic stages), and are therefore expected to be the choosier
sex. Males, on the other hand, are expected to be less choosy, especially in lekking species where males contribute nothing but sperm to
reproduction. In these latter species males have often been found to mate
indiscriminately with as many receptive females as possible. In contrast, our
study of the haplochromine cichlid fish Astatotilapia flaviijosephi, a
maternal mouth-brooder, provides the first experimental evidence for male mate
choice in a lekking species. In this species the
number of eggs spawned correlates positively with female weight, thus, making
larger females potentially better mates. Our experiments indeed demonstrated
that A. flaviijosephi males prefer to court the
larger of two females when given a simultaneous choice. Furthermore, males
spent more time courting during experimental trials involving larger females.
This selective allocation of courtship effort to more attractive (i.e. heavier)
females suggests that there may be constraints on males in fertilizing multiple
females, thus compelling them to be choosy.
Lotem A, Fishman M.A., & Stone L.
2003 From reciprocity to unconditional altruism through signaling benefits. Proc.
Roy. Soc. Lond. B. 270:199-205. (PDF version).
Abstract: Cooperation among
genetically unrelated individuals is commonly explained by the potential for future
reciprocity or by the risk of being punished by group members. However,
unconditional altruism is more difficult to explain. Here we show that
unconditional altruism can evolve as a costly signal of individual quality
(i.e. a handicap) as a consequence of reciprocal altruism. This is because the
emergent correlation between altruism and individual quality in reciprocity
games can facilitate the use of altruism as a quality indicator in a much wider
context, outside the reciprocity game, thus affecting its further evolution
through signaling benefits. Our model, based on multitype
evolutionary game theory, shows that when the additive signaling benefit of
donating help exceeds the cost for only some individuals (of high quality
state) but not for others (of low quality state), the population possesses an
ESS profile wherein high quality individuals cooperate unconditionally while
low quality individuals defect or play TfT. Hence, as
predicted by Zahavi’s
handicap model, signaling benefits of altruistic acts can establish a stable
generosity by high quality individuals which no longer depends on the
probability of future reciprocation or punishment.
Ovadia O, Pinshow B. & Lotem A.
2002 Thermal imaging of house sparrow nestlings: the effect of begging behavior
and nestling rank. The Condor 104:837–842. ( PDF
version)
Abstract: We used infrared imaging to test whether the energetic
cost of begging is observable in changes in body surface temperature (Ts) of
young House Sparrow nestlings (Passer domesticus),
and whether Ts is affected by nestling rank. Begging had a mixed effect on Ts,
increasing it slightly at first, but decreasing it when hungry nestlings begged
more vigorously. This mixed effect may result from heat production being
quickly offset when begging posture and movement enhance heat loss through the
skin, and suggests that the energetic cost of begging cannot be inferred from
thermal imaging. The analysis of Ts in relation to nestling rank showed that
although low-ranked nestlings maintained lower Ts than their larger siblings,
their Ts was higher than expected for their body mass.
This suggests that nestlings of a lower rank may gain heat from their larger,
more developed nestmates.
Fishman M.A., Lotem A & Stone L. 2001 Heterogeneity
stabilizes reciprocal altruism interactions. J. Theor.
Biol. 209, 87-95. (PDF version)
Abstract: In considering the phenomena of reciprocal altruism few
would dispute that there are differences in individual quality-in particular,
that for some individuals, at least on occasion, the cost of doing favors will
exceed the potential of future benefits. That is, at any given time, a typical
population is heterogeneous with respect to the affordability of reciprocal
altruism. However, methodological limitations of the traditional analytical
framework-Single Type (symmetric) Evolutionary Game Theory-have restricted previous
analytical efforts to addressing populations idealized in terms of their
averages. Here we use the methods of Multitype
Evolutionary Game Theory to analyze the role of individual differences in
direct reciprocity interactions. Multitype analysis
shows that non-idealized populations possess an ESS profile wherein individuals
who cannot afford reciprocity (low quality) defect, while individuals who
derive net benefits from reciprocity (high quality) cooperate. Furthermore,
this cooperation is implemented via unmodified Tit-for-Tat strategy. Hence our
results may help resolve a long-standing problem concerning the evolutionary
stability of Tit-for-Tat in direct reciprocal altruism. Finally, this
difference between idealized and real populations is not restricted to direct
reciprocal cooperation. Previously (Lotem et al., 1999) we have demonstrated
evolutionary stable indirect reciprocal cooperation among high quality
individuals in heterogeneous populations.
Kedar H., Rodriguez-Girones M., Yedvab S., Winkler DW & Lotem A. 2000. Experimental evidence for offspring learning in parent-offsrping communication. Proc. Roy. Soc. Lond. B. 267, 1723-1727. (PDF
version)
Abstract: The offspring of birds and mammals solicit food from
their parents by a combination of movements and vocalizations that have come to
be known collectively as `begging'. Recently, begging has most often been
viewed as an honest signal of offspring need. Yet, if offspring learn to adjust
their begging efforts to the level that rewards them most, begging intensities
may also reflect offsprings' past experience rather
than their precise current needs. Here we show that bird nestlings with equal
levels of need can learn to beg at remarkably different levels. These
experiments with hand-raised house sparrows (Passer domesticus)
indicated that chicks learn to modify begging levels within a few hours.
Moreover, we found that the begging postures of hungry chicks in natural nests
are correlated with the average postures that had previously yielded them parental feedings. Such learning challenges parental
ability to assess offspring needs and may require that, in response, parents
somehow filter out learned differences in offspring signals.
Lotem A., Fishman A. M., & Stone L. 1999. Evolution of
cooperation between individuals.Nature
400:226-227. (PDF version) (see http://lynx.tau.ac.il/coop.html
for an electronic appendix)
Abstract: Nowak and Sigmund(1) conclude
that cooperation may have evolved through indirect reciprocity by image
scoring. Their simulations and analytical models(1,2)
predict long term cyclical dynamics between cooperative and defector
populations rather than an evolutionarily stable equilibrium. Here we add a
realistic feature to their model: that there are always some individuals unable
to cooperate owing to their poor phenotypic condition (we call these
individuals ('phenotypic defectors'). The presence of phenotypic defectors
paradoxically allows persistent discriminating cooperation under a much wider
range of conditions than found by Nowak and Sigmund because there is selection
against both defection and unconditional altruism. In real populations there
will nearly always be some level of defection because phenotypic defectors such
as the young, sick or handicapped) may be unable to
help even if they have a genetic predisposition to do so.
Rodriguez-Gironez M., Lotem A. 1999,
How to detect a cuckoo egg: a signal detection theory model for recognition and
learning. Amer. Natur. 153: 633-648. (PDF version)
Abstract: This article presents a model of egg rejection in cases
of brood parasitism. The model is developed in three stages in the framework of
signal-detection theory. We first assume that the behavior of host females is
adapted to the relevant parameters concerning the appearance of the eggs they
lay. In the second stage, we consider the possibility that females make
perceptual errors. In the final stage, females must learn to recognize their
own eggs through an imprinting process. The model allows us to make a number of
predictions concerning the egg types that should be rejected in different
circumstances: egg rejection should increase as the parasitism rate increases
and egg mimicry deteriorates; host females' erroneous ejection of their own
eggs should be expected for intermediate levels of egg mimicry but not for very
good or very poor mimicry; host females would benefit most from learning to
recognize their own eggs when individual variability in egg characteristics is
much lower than the population variability; and, when egg mimicry is poor or
individual variability is very low, females should attempt to imprint on the
first egg they lay, before they can be parasitized, but, when mimicry is good
and individual variability is relatively high, females must use an extended
learning phase. The model provides a framework to study how the enigmatic
acceptance of parasitic eggs can be explained by adaptive discrimination
mechanisms.
Lotem A. Wagner R.H. & Balshine-Earn
S. 1999, The overlooked signaling component in
non-signaling behavior. Behavioral Ecology. 10:
209-212. (PDF version)
Abstract: Despite the general acceptance that the handicap
principle explains extravagant morphological and behavioral signals, the
model's mechanism has not been applied to explain quantitative variations in
non-signaling behaviors. We suggest that animals may be selected to perform
many behaviors differently when they are observed by other animals, and that
such changes in the level or the intensity of a behavior can shift the behavior
from its non-signaling optimum. As a result, many behaviors that are not
defined as signals may nevertheless evolve a signaling component that affects
them quantitatively rather than qualitatively. We explore this issue using
examples from prey fleeing from a predator, human behavior in the presence of
others, and parental care behavior. We then apply the overlooked signaling
component of behaviors to illustrate that helping behavior among kin, which
increases inclusive fitness, also may eventually evolve into signals of
individual quality, condition, or need.
Lotem A. 1999 Manipulative begging by parasitic cuckoo
nestlings and paradoxical host behaviour: a reply to
Redondo. Trends in Ecology and Evolution. 14: 107. (PDF version)
Abstract: I welcome Redondo's clarification that Davies et al.'s
new finding(1) can be viewed as a specific case of his Manipulative
Interference Model(2) (MIM). My suggestion that Davies et al.'s study provides
a 'different answer' related to the precise way in which cuckoo chicks
manipulate their hosts, not in questioning whether they do so. Regarding the
title question of my article 'Why should true offspring not do the same?': there is no doubt that because of the lack of genetic
relatedness parasitic nestlings are expected to beg
more(3-5). However, because we cannot feasibly predict how much more, we cannot
determine if this is the only reason; perhaps there are additional ones. Being
satisfied with the immediate and obvious explanation, as suggested by Redondo,
might not be the most productive methodology, because it weakens the motivation
to consider alternatives or to look for additional factors…..
Lotem A. 1998. Manipulative begging calls by parasitic cuckoo
chicks: why should true offspring not do the same? Trends
in Ecology and Evolution. 13: 342-343. (PDF version)
Abstract: The long-standing puzzle of how cuckoo chicks deceive
their foster parents(1-4) continues to challenge
evolutionary biologists. Although the host's inability to discriminate among
nestlings can be explained as a result of an evolutionary lag(1-3)
or learning constraints(5), the tendency to feed any nestling at the nest does
not explain how the single chick of the common cuckoo (Cuculus
canorus) extracts food from its foster parents at a
rate comparable to that of a whole brood of host young(6). A new study(7),
using reed warbler hosts (Acrocephalus scirpaceus), suggests that cuckoo chicks trick their foster
parents by using begging calls that mimic the sound of a whole brood. This
finding provides an exciting explanation for how the cuckoo deceives its host
but also challenges our view of nestling begging as honest signals of offspring
need(8,9). If cuckoo chicks can use manipulative
begging calls, why have normal chicks not evolved similar adaptations to
exploit their parents? Although there are certain hints in the literature that
suggest possible answers, the issue is still unresolved.
Lotem A. 1998. Differences in begging behaviour among barn swallow (Hirundo
Rustica) nestlings. Anim. Behav. 55:809-818. (PDF version)
Abstract: Recent models of parent-offspring communication suggest
that nestling begging reliably reflects food requirements, and therefore should
increase with nestling need. Need may be affected by short-term variations in
hunger, as well as by long-term factors such as relative size, growth rate and
body condition. In the present study, the brood sizes of barn swallows were
manipulated to create differences in nestling growth rate and body condition.
The extent to which begging behaviour reflects these
differences was tested. I measured begging behaviour
by removing nestlings from the nest for three laboratory tests in which
temporal variations in hunger were controlled, and four target nestlings (small
and large, from small and large broods) were tested simultaneously. Small
nestlings and nestlings from large broods had lower growth rates and poorer
body condition than large nestlings and nestlings from small broods,
respectively. Begging was positively correlated with both short- and long-term
determinants of need. However, when nestlings grew older (second test), the
trend was mixed, mainly because begging levels dropped in the neediest nestling
category (small nestlings from large broods). After nestlings had been
exchanged between broods for 24 h, small nestlings from large broods improved
their growth rate and body condition, but still begged less than expected from
their long-term need. The results suggest that nestling begging strategies vary
with brood size and with nestling rank. However, these variations may reflect
not only long-term need, but also nestling response to past experience or to
variations in the cost and effectiveness of their begging efforts.
Lotem A. 1998. Brood reduction and begging behaviour
in the Swift Apus apus; no evidence that large nestlings restrict
parental choice. Ibis 140:507-511.
Abstract: Brood reduction in birds is generally viewed as an
adaptive process by which parents can maximize reproductive success in the face
of an unpredictable environment. However, brood reduction may not be adaptive
for the parents if the reduction is instead caused by large nestlings that
block the nest entrance, thereby restricting parental choice, To determine the
degree of difficulty faced by the parents in obtaining access to their smallest
nestlings, a simple experiment was conducted in the Swift Apus
apus. By inserting a human hand blindly into Swift
nesting holes, nestlings were stimulated to beg and to grasp the approaching
fingers. The results show that the smallest nestlings in the nest were the
first to encounter the approaching fingers. Small nestlings were also just as
likely to be found with at least some food in their crops as were medium and
large nestlings, but gained mass at a significantly slower rate. I suggest that
parent Swifts can easily access small nestlings, but prefer either to allocate
more food to larger nestlings or to allow sibling competition in order to facilitate
brood reduction.
Lotem A. 1998. Higher levels of begging behavior by small
nestlings: a case of a negatively correlated handicap.
Abstract: Recent theoretical models of parent-offspring conflict
suggest that costly solicitation by offspring reflects offspring need in a
reliable manner, and that parents are, therefore, selected to increase parental
effort in response to offspring solicitation. However, theory and experiments
suggest that parents pay attention not only to their nestlings' needs, but also
to their relative quality as reflected by size and competitive ability. A study
on barn swallow nestlings, described here, investigates how such complex
feeding rules affect nestling begging strategies, and how different begging
strategies affect the nestlings' relative success. Begging strategies were
compared for large and small brood mates, assumed to represent high and low
nestling qualities, respectively. The results indicate that small nestlings
tend to beg at greater intensities than large nestlings for a similar level of
food deprivation. A-higher intensity of begging does not, however, guarantee
greater success for smaller nestlings because mass gain by nestlings is
affected by both size and begging differences among the competing nestlings. I
suggest that higher levels of begging by small nestlings are caused by
differences in the expected benefit for a given level of begging, and create a
negative correlation between the optimal level of signaling and the signaler's
quality. This contrasts with the typical handicap case discussed in the
literature, in which differences among individuals in the cost of signaling
create a positive correlation between the optimal level of signaling and the
signaler's quality. This study suggests that "negatively correlated
handicaps" may emerge whenever receivers integrate cryptic information
about the signaler's momentary need or motivation, based on one signal, and
non-cryptic information about the signaler's quality based on other cues.
Balshine-Earn S., Lotem A. 1998. Experimental evidence for individual recognition from video
playbacks in a cooperatively breeding cichlid (Neolamprologus
brichardi). Behaviour
135:1-18 PDF
VERSION
Abstract: Most theories of social behaviour
and cooperation assume that animals can recognise
other individuals, but this is rarely tested. Using Neolamprologus
brichardi, a cooperatively breeding cichlid fish, we
monitored behavioural responses to (1) real fish
versus video images of fish; (2) mate versus neighbour
and (3) video images of mate versus video image of neighbour.
All tests were controlled for size and sex. Fish reacted appropriately to the
playbacks, although responses to videos were not as strong as to real fish.
Both males and females fought against the images of stranger and neighbour fish and they courted images of mates. These results
confirm that the cooperatively breeding fish, Neolamprologus
brichardi, recognises
individuals based on vision and that video playbacks contain sufficient
information to facilitate recognition.
Rodriguez-Gironez
M., Lotem A. 1998. Acceptance by the splendid fairy-wren of
parasitism by Horsfield's bronze-cuckoo:
re-examination of Brooker and Brooker
equilibrium model. Behavioral Ecology 9:419-420. PDF
VERSION
Abstract: Brooker and Brooker (1996) have recently published data from a 17 year
study of a splendid fairy-wren (Malurus splendens) population parasitized by Horsfield's
bronze-cuckoo (Chrysococcyx basalis)
in Western Australia. They argue that "of the two explanations for the
lack of rejection, neither really stands up to scrutiny with respect to the
splendid fairy-wren" (p. 396). Instead, they propose a new model for
evolutionary equilibrium based on the life history and population structure of
the host species. According to their model, pure acceptance of parasitic eggs
and chicks is an evolutionarily stable strategy (ESS, Maynard Smith and Price,
1973) regardless of how costly rejection of parasitic eggs might be. While we
endorse the use of equilibrium models in the study of avian brood parasitism,
we find some problems in the specific model proposed by Brooker
and Brooker. Namely, we suspect that their model
cannot be stable.
Lotem A., & Nakamura H., 1998.
Evolutionary equilibria in Avian
brood parasitism: an alternative for the "arms race-evolutionary lag"
concept. In Parasitic birds and their hosts: studies in coevolution.
Ed. by S.I. Rothstein and S.K. Robinson, pp. 223-235.
Abstract: Based on a review of the literature, this paper
investigates whether avian brood parasitism systems are continuously coevolving
as in an arms race, or rather they are in an evolutionary equilibrium. Under
the "arms race" view, the acceptance of parasitic eggs or nestlings,
which reduces host fitness, is a result of an evolutionary lag in the development
of counter adaptations by the host.. Under the
equilibrium view, acceptance is an inevitable result of an
equilibrium among various selective pressures. The possible costs and
benefits of egg rejection are summarized in a model, and some possible ways in
which an equilibrium might be expressed in a host
population are suggested. Available data on avian brood parasitism are
discussed in relation to the equilibrium hypothesis; Direct
measurements of rejection costs and benefits rarely provide conclusive results
but suggest that in many systems an equilibrium is as reasonable an
interpretation as evolutionary lag. Evidence for adaptive rules in the
occurrence of rejections and acceptances within a host population provides the
strongest support for the equilibrium model. Comparative evidence previously
explained by the arms race model, is shown here to fit the equilibrium model as
well.
Lotem A. & Rothstein S.I. 1995.
Cuckoo-host coevolution: from snapshots of an arms
race to the documentation of microevolution. Trends in Ecology and Evolution
10:436-437. (PDF version)
Abstract: It is not often that a notable study in evolutionary
biology published in Nature has nearly all of its assumptions and conclusions
challenged by a second paper. But this is precisely what happened when Zuniga
and Redondo1 questioned Soler and Moller's2 work on coevolution between the brood parasitic great spotted
cuckoo (Clamator glandarius)
and its magpie (Pica pica) host.
Lotem A., Nakamura H. & A. Zahavi.
1995. Constraints on egg discrimination and cuckoo-host coevolution.
Anim. Behav. 49:1185-1209. (PDF version)
Abstract: To understand the co-existence of rejection and
acceptance of cuckoo eggs within a host population, the mechanism of egg
discrimination and the cost-benefit balance of rejection behaviour
were investigated. At a study site in central Japan, rejection rate of cuckoo, Cuculus canorus, eggs by great
reed warblers, Acrocephalus arundinaceus,
was 61·5%. An analysis of host response to natural and experimental parasitism
with real cuckoo eggs, cuckoo egg models and painted host eggs indicated that:
(1) hosts are more likely to reject eggs that look different from their own;
(2) almost all individuals (94%) can reject highly non-mimetic eggs, suggesting
that there are few, if any, true accepter genotypes in the host population; (3)
hosts usually reject by egg ejection; (4) during the host-laying period, the
day of parasitism does not affect host response; (5) egg types that were
rejected at lower rates also took longer to be rejected; (6) acceptance was
more likely to occur among mid-season breeders which consist of a higher
proportion of younger females in the host population. Two experiments indicated
that previous exposure of a host to its own eggs affects its rejection behaviour, suggesting that a learning mechanism (an
imprinting-like process) is involved. Parasitized nests from which the cuckoo
egg was experimentally removed, or ejected by hosts, fledged more host young
than nests in which the cuckoo egg was accepted. Hosts that deserted
parasitized nests were likely to re-nest, and the success of re-nests was high.
Costs due to breakage of host eggs occurred in only 3·5% of successful cuckoo
egg ejections. A cost-benefit model of egg rejection suggests that under some
circumstances, the cost of recognition errors may exceed that of parasitism.
Egg variability within a clutch was higher among younger females. Some hosts
rejected painted eggs and conspecific eggs based on
differences that may occur naturally within variable clutches of other
individuals. It is suggested that host egg variability is a major constraint on
the learning mechanism of egg recognition. Accordingly, the cost of mistakenly
rejecting an odd egg from the nest selects for greater tolerance towards
divergent eggs in young breeders, and justifies a prolonged learning mechanism
in which a host can learn to recognize the variation range of its own eggs. The
co-existence of rejection and acceptance within the host population can
therefore be explained as a compromise between the cost of parasitism and the
cost of recognition errors, rather than as an evolutionary lag. This
explanation is particularly pertinent where the cuckoo has evolved mimetic eggs
and where the parasitism rate is low.
Lotem A. 1993. Secondary sexual ornaments as signals: the
handicap approach and three possible problems. Ethologia
3:209-218. Proceedings of the XXIII International Ethological
Conference,
Abstract: Secondary sexual ornaments have recently been discussed
in the context of biological signals, and the handicap principle has been
suggested as a model explaining their evolution. The handicap principle
predicts that at equilibrium, sexual ornaments will be honest signals of the
male's quality. This is because the cost of ornaments to a potential cheater (a
low quality male) will be greater than to an honest signaler (a high quality
male), to an extent that makes cheating maladaptive. Accordingly, the cost of
the ornament (the handicap) should be related to the quality it reveals. In the
following, I discuss three problems with the handicap approach: i) It is difficult to determine
the cost of the handicap and the quality it reveals. Nevertheless, I suggest that
it is feasible and is worth doing. ii) It is not clear whether phylogenetic data can be used to distinguish between the
handicap model and the sensory exploitation model. I suggest that it can be
used only under restricted conditions. iii) Cheating (dishonest signalling) seems to contradict the handicap model. I will
try to show, however, that some forms of cheating can be explained by the
handicap model.
Lotem A. 1993. Learning to recognize nestlings is maladaptive
for cuckoo Cuculus canorus
host. Nature 362:743-745. (PDF
version)
Abstract: The picture of a tiny passerine host feeding a huge
cuckoo nestling challenges evolutionary biologists who explain animal behaviour as adaptive(1-4). Cuckoo
eggs sometimes resemble the eggs of the host, but nestlings of the common
cuckoo, Cuculus canorus,
look very different from the young of the host. The inability of the host to
discriminate against such divergent nestlings is especially puzzling as some
cuckoo hosts show a finely tuned discrimination ability between eggs(5-8). Here I present a simple model to explain this
paradox. The model shows that although learning to recognize eggs is adaptive,
learning to recognize nestlings might not be. The mechanism of learned
recognition, previously shown to maintain egg recognition, is unlikely to be
adaptive for hosts like those of the common cuckoo, in which only the parasitic
nestling remains in the nest. The reason that discrimination against parasite
nestlings is not adaptive is that the cost of misimprinting
(learning to recognize the parasite nestling as the parents' own) exceeds the
benefit of correct learning. The model also explains why nestling
discrimination is mostly found in host-parasite systems in which the parasite
and the hosts' young are reared together(1).
Lotem A., Nakamura H. & A. Zahavi. 1992.
Rejection of cuckoo eggs in relation to host age: a possible evolutionary
equilibrium. Behavioral Ecology 3:128-132. PDF VERSION
Abstract: Because hosts that accept a parasitic egg laid by the
common cuckoo, Cuculus canorus,
are unlikely to fledge their own offspring, rejection should be an adaptive
response. Evidence that cuckoo host species attain only
intermediate rates of rejection are commonly interpreted as resulting from an
evolutionary lag. Yet, we found that the acceptance of cuckoo eggs by
female great reed warblers, Acrocephalus arundinaceus, occurs mainly among the younger breeders in
the host population. We suggest that some level of acceptance can arise in the
host population as a result of the need of naive breeders to learn to reliably
recognize their own eggs rather than representing evolutionary lag.
Lotem A., Schechtman E. & G.
Katzir. 1991. Little egrets' Egretta garzetta capture of
submerged prey: Strike depth, strike angle and possible effects of light
refraction. Anim. Behav. 42:341-346. PDF VERSION
Abstract: How little egrets catch submerged prey was observed in
the field. The proportion of successful strikes was measured relative to the
angle and depth of the strike and the water level in the pond. Prey capture
success was significantly related to strike angle, being highest at the most
acute angles. Strike depth had no effect on capture success. Strikes were more
successful in shallow streams than in full or partly drained ponds. Adult
breeding birds were as successful as non-breeders and juveniles, but performed
deeper strikes more often. There was also significant variation between
individuals in capture success. Light refraction had no apparent effect on the
egrets' capture success.
Katzir, G., Lotem, A. & N. Intrator. 1989. Stationary underwater prey missed by reef
herons, Egretta gularis:
head position and light refraction at the moment of strike. J. Comp.
Physiol. A. 165:573-576. PDF VERSION
Abstract: This paper attempts to verify the importance of spatial
positioning of the eyes of reef herons Egretta gularis schistacea, when coping
with light refraction at the air-water interface. The herons' striking of prey,
while their approach angle was restricted, was observed. (a) The herons'
capture success in the restricted situation was markedly lower than in the
unrestricted situation. (b) The points of strike (STR) in unsuccessful strikes
differed from those of successful strikes, and from those of the unrestricted
situation. (c) The larger the differences between the observed and the
predicted ratio of prey depth to apparent prey depth, the higher the
probability of missing a prey. These results support predictions of a model
presented elsewhere (Katzir and Intrator
1987) that a heron will attempt to reach spatial positions at which prey's real
depth and apparent depth are linearly correlated.
Return to my home page