Uzi Motro

Kin selection and strong evolutionary stability of mutual help.

The theory of kin selection, as developed by Hamilton (e.g., 1964, 1970) stems from the fact that in a sexually reproducing population, the genotype of a progeny of an individual is not necessarily identical to the genotype of either parent. Thus natural selection cannot operate through the preservation of the most tit type. Instead, it can only be expressed in terms of changes in gene frequencies. Such changes, as suggested by Hamilton, are likely to be in favor of those genes which, by their effect on their carriers, act to increase the expected number of their copies in the population of the next generation. Thus, in Hamilton’s terminology, natural selection is expected to favor genes which increase their carrier’s inclusive fitness (e.g., Hamilton, 1964). More specifically, it has been maintained by Hamilton that if, in order to save a kin of relatedness r (see Wright, 1922), a risk of 0 <x < 1 is needed, then, by taking this risk, an individual will add a value of r---x to its inclusive fitness. Taking such a risk will, therefore, be selected for if and only if x ,< r, and the value r is expected to be the maximal risk accepted by an individual in a population in order to save a relative of relatedness r. This prediction is, however, not always in a satisfactory agreement with empirical observations, a discrepancy that provoked some attacks on the very theory of kin selection (e.g., Zahavi, 1981). For example, parents’ help to their offspring is almost always more generous than offspring’s help to their parents or to their sibs, even though the relatedness in both cases is the same. Moreover, even on a theoretical level, the prediction mentioned above cannot possibly be true, for example, on an isolated island, overpopulated by

Dinoflagellate-Cyanobacterium Communication May Determine the Composition of Phytoplankton Assemblage in a Mesotrophic Lake

The reasons for annual variability in the composition of phytoplankton assemblages are poorly understood but may include competition for resources and allelopathic interactions. We show that domination by the patch-forming dinoflagellate, Peridinium gatunense, or, alternatively, a bloom of a toxic cyanobacterium, Microcystis sp., in the Sea of Galilee may be accounted for by mutual density-dependent allelopathic interactions. Over the last 11 years, the abundance of these species in the lake displayed strong negative correlation. Laboratory experiments showed reciprocal, density-dependent, but nutrient-independent, inhibition of growth. Application of spent P. gatunense medium induced sedimentation and, subsequently, massive lysis of Microcystis cells within 24 hr, and sedimentation and lysis were concomitant with a large rise in the level of McyB, which is involved in toxin biosynthesis by Microcystis. P. gatunense responded to the presence of Microcystis by a species-specific pathway that involved a biphasic oxidative burst and activation of certain protein kinases. Blocking this recognition by MAP-kinase inhibitors abolished the biphasic oxidative burst and affected the fate (death or cell division) of the P. gatunense cells. We propose that patchy growth habits may confer enhanced defense capabilities, providing ecological advantages that compensate for the aggravated limitation of resources in the patch. Cross-talk via allelochemicals may explain the phytoplankton assemblage in the Sea of Galilee.

Avoiding Inbreeding and Sibling Competition: The Evolution of Sexual Dimorphism for Dispersal

Natal dispersal can reduce sibling competition and the risk of inbreeding, but it may also confer a personal cost on the disperser. A simple gene-frequencies model is presented, which takes into consideration the effects of both competition and inbreeding avoidance on the evolution of dispersal. The evolutionarily stable strategies of dispersal are obtained, and the possibility of sexual dimorphism with regard to dispersal behavior is analyzed. If the cost of inbreeding is low, both sexes adopt the same dispersal strategy, whereas if the cost of inbreeding is high enough, we can expect to find sexual dimorphism with respect to dispersal behavior (even if both sexes have the same costs and benefits associated with dispersal).

Optimal rates of dispersal II. Diploid populations

The problem of how an individual should divide its progeny into dispersed and non-dispersed descendants is investigated for a number of haploid models. In each model, a unique optimal ratio of dispersed to non-dispersed has been found, where the type with this optimal strategy has a selective advantage over all other types. Although the survival ability of a dispersed offspring is reduced (compared to that of a non-dispersed offspring), the optimal strategy implies that a substantial part of the progeny will be dispersed.

DO FEMALE CHACMA BABOONS COMPETE FOR A SAFE SPATIAL POSITION IN A SOUTHERN WOODLAND HABITAT

In this study troop of chacma baboons (Papio cynocephalus ursinus) at Mkuzi Game Reserve, Zululand, South-Africa, it is suggested that risk of predation and competition over safe spatial position had more importance and effect on female behaviour than did competition for food. Only 6.4% of all agonistic events were over food patches and no significant correlation was found between a females dominance rank and proportion of time spent feeding, feeding bout length or diet composition. Parameters of reproductive success, such as inter-birth intervals and infant mortality were not correlated with female dominance rank. Female mortality, however, was related to dominance rank and all of the five females who disappeared during the study were low-ranking. Four of the five females disappeared after troop fission. There is circumstantial evidence supporting the suggestion that predation by leopards is the main cause of mortality of females at Mkuzi. High levels of female aggression were recorded, with almost no occurrences of support coalitions. Most of the aggression took place among similar ranking females, or was directed by the top ranking toward the lowest ranking females. Most of the female-to-female agonistic encounters were in a social context, and more than half were over a spatial position next to other adult troop members. Aggression among females increased after troop fission. It is suggested that the higher-ranking females may be better protected from predation, through access to more central spatial positions in the troop. Indeed, a positive correlation was found between a females dominance rank and the time spent next to other adult troop members. It may be that avoiding food competition by keeping larger distances from others, while foraging, was translated in lower ranking females to a cost of higher predation risk.

The Three Brothers' Problem: Kin Selection with More than One Potential Helper. 1. The Case of Immediate Help

In situations involving a single relative in distress and several potential helpers, the advantage of leaving the risky job of aiding the relative in need to any of the other potential helpers is quite obvious. Hence, even if Hamiltons condition for altruism in the one-to-one situation is satisfied, it might seem that altruistic behavior would not evolve if there is more than one potential helper. In this paper we investigate the evolutionarily stable strategy (ESS) of helping behavior in situations involving several potential helpers and a necessarily instantaneous response. The main result is that if Hamiltons condition is met, the ESS is usually a mixed strategy of altruism and selfishness, with a decreasing (yet positive) probability of helping as the number of potential helpers increases.

Molecular analysis of HLA class II polymorphisms among different ethnic groups in Israel

The Jewish population in Israel comprises of inhabitants of heterogeneous ethnic backgrounds. Genetic studies classify the Israeli Jewish population into two major groups: Ashkenazi from Central and Eastern Europe and Sephardic or non Ashkenazi, from the Mediterranean and North Africa. The present study was aimed at elucidating the differential influx of HLA class II alleles in Ashkenazi, in various non-Ashkenazi subgroups and in Israeli Moslem Arabs. Using the PCR-SSOP technique, a large number of alleles were detected at each of the loci examined (DRB1, DQA1 and DQB1). In addition, gene frequencies, characteristic DR/DQ linkage disequilibria, population distance and their corresponding dendogram, were used to study the relationship between Israelis as a group, non Jewish Caucasians and Blacks. These populations could be grouped into three main clusters: the first consists of all the Israeli groups with the exception of the Ethiopian Jews; the second consists of non Jewish Caucasians, with a clear distinction seen between Israelis and non Jewish Europeans and U.S. Caucasians; the third, composed of Blacks, is distinctly different from the other populations. Ethiopian Jews were found to be closer to the Blacks than to any of the Israeli Jewish groups. We have shown that Jews share common features, a fact that points to a common ancestry. A certain degree of admixture with their pre-immigration neighbors exists despite the cultural and religious constraints against intermarriage.

Early experience affects producer–scrounger foraging tendencies in the house sparrow

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 individuals 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.

Innate movement rules in foraging bees: flight distances are affected by recent rewards and are correlated with choice of flower type

Abstract The non-random movement patterns of foraging bees are believed to increase their search efficiency. These patterns may be innate, or they may be learned through the bees’ early foraging experience. To identify the innate components of foraging rules, we characterized the flight of naive bumblebees, foraging on a non-patchy “field” of randomly scattered artificial flowers with three color displays. The flowers were randomly mixed and all three flower types offered equal nectar volumes. Visited flowers were refilled with probability 0.5. Flight distances, flight durations and nectar probing durations were determined and related to the bees’ recent experiences. The naive bees exhibited area-restricted search behavior, i.e., flew shorter distances following visits to rewarding flowers than after visits to empty flowers. Additionally, flight distances during flower-type transitions were longer than flight distances between flowers of the same type. The two movement rules operated together: flight distances were longest for flights between flower types following non-rewarding visits, shortest for within-type flights following rewarding visits. An increase in flight displacement during flower-type shifts was also observed in a second experiment, in which all three types were always rewarding. In this experiment, flower-type shifts were also accompanied by an increase in flight duration. Possible relationships between flight distances, flight durations and flower-type choice are discussed.

Evolutionary and Continuous Stability in Asymmetric Games with Continuous Strategy Sets: The Parental Investment Conflict as an Example

In a population that is fixed at an evolutionarily stable strategy (ESS), no mutant strategy can invade and spread. If, however, the strategy set is continuous, one can ask which mutations can be established in a population that is fixed not at an ESS but, rather, at a different, nearby strategy. This question gives rise to a possible distinction between the various ESSs with respect to their dynamic stability characteristics and is treated here for the case of asymmetric games. Two distinct types of ESSs can exist in such games: ESSs that are continuously stable (CSSs) and ESSs that are not. Any strategy in the neighborhood of a continuously stable ESS can always be invaded by mutants that are closer to the ESS. In contrast, any neighborhood of an ESS that is not a CSS contains a nonzero measure set of strategies that are not immune to any mutation that is further away from the ESS. Thus, in natural situations, one can expect more frequently to find populations at (or near) an ESS that is a CSS than at (or near) an ESS that is not continuously stable. The ideas are illustrated by two examples, the parental investment conflict and the dispersal conflict between males and females.