植物亲缘识别的研究进展

植物的亲缘识别(kin recognition)指植物通过识别周边个体与自己的亲缘关系, 调整自身的生长生态策略、促进亲缘个体的生存与繁衍。研究表明, 植物主要通过特定的叶片挥发物、根系分泌物、感光载体等途径, 识别周边个体与自己的亲缘关系, 改变自身形态学策略(如根系大小、根冠比、种子数量等)或者生理代谢策略(次生代谢物质、防御蛋白等), 调整与周边个体的竞争强度, 缓和与近亲缘个体之间的竞争, 加强与远亲缘或非亲缘个体的竞争。同时亲缘识别的强度也受环境因子(养分等)的影响。结合目前的研究进展, 该文分析了导致亲缘识别的研究结果存在差异或争议的主要原因, 认为主要与实验材料的选择、亲缘关系的界定标准、环境条件及测定的指标不统一有关。将来的研究应重点从生理生化、分子、代谢水平上深入研究植物亲缘识别的机理。     

Kin recognition in an annual plant

Kin recognition is important in animal social systems. However, though plants often compete with kin, there has been as yet no direct evidence that plants recognize kin in competitive interactions. Here we show in the annual plant Cakile edentula, allocation to roots increased when groups of strangers shared a common pot, but not when groups of siblings shared a pot. Our results demonstrate that plants can discriminate kin in competitive interactions and indicate that the root interactions may provide the cue for kin recognition. Because greater root allocation is argued to increase below-ground competitive ability, the results are consistent with kin selection.     

Nepotistic cooperation in non-human primate groups

Darwin was struck by the many similarities between humans and other primates and believed that these similarities were the product of common ancestry. He would be even more impressed by the similarities if he had known what we have learned about primates over the last 50 years. Genetic kinship has emerged as the primary organizing force in the evolution of primate social organization and the patterning of social behaviour in non-human primate groups. There are pronounced nepotistic biases across the primate order, from tiny grey mouse lemurs (Microcebus murinus) that forage alone at night but cluster with relatives to sleep during the day, to cooperatively breeding marmosets that rely on closely related helpers to rear their young, rhesus macaque (Macaca mulatta) females who acquire their mother''s rank and form strict matrilineal dominance hierarchies, male howler monkeys that help their sons maintain access to groups of females and male chimpanzees (Pan troglodytes) that form lasting relationships with their brothers. As more evidence of nepotism has accumulated, important questions about the evolutionary processes underlying these kin biases have been raised. Although kin selection predicts that altruism will be biased in favour of relatives, it is difficult to assess whether primates actually conform to predictions derived from Hamilton''s rule: br > c. In addition, other mechanisms, including contingent reciprocity and mutualism, could contribute to the nepotistic biases observed in non-human primate groups. There are good reasons to suspect that these processes may complement the effects of kin selection and amplify the extent of nepotistic biases in behaviour.     

Demography and the tragedy of the commons

Individual success in group‐structured populations has two components. First, an individual gains by outcompeting its neighbours for local resources. Second, an individual's share of group success must be weighted by the total productivity of the group. The essence of sociality arises from the tension between selfish gains against neighbours and the associated loss that selfishness imposes by degrading the efficiency of the group. Without some force to modulate selfishness, the natural tendencies of self interest typically degrade group performance to the detriment of all. This is the tragedy of the commons. Kin selection provides the most widely discussed way in which the tragedy is overcome in biology. Kin selection arises from behavioural associations within groups caused either by genetical kinship or by other processes that correlate the behaviours of group members. Here, I emphasize demography as a second factor that may also modulate the tragedy of the commons and favour cooperative integration of groups. Each act of selfishness or cooperation in a group often influences group survival and fecundity over many subsequent generations. For example, a cooperative act early in the growth cycle of a colony may enhance the future size and survival of the colony. This time‐dependent benefit can greatly increase the degree of cooperation favoured by natural selection, providing another way in which to overcome the tragedy of the commons and enhance the integration of group behaviour. I conclude that analyses of sociality must account for both the behavioural associations of kin selection theory and the demographic consequences of life history theory.     

Queen number and genetic relatedness in a neotropical wasp, Polybia occidentalis

We found that genetic relatedness among Polybia occidentalisworkers was .26±0.057, a value high enough to make altruisticbehavior by workers relatively easy to explain. This comparativelyhigh level of relatedness can be attributed to close relatednessamong queens of .57±0.077 and to great variation amongcolonies in numbers of queens. The harmonic mean of queen numberis 3.1 queens per colony, which is much lower than the arithmeticmean of 10.6 queens per colony. These results are consistentwith a colony cycle called cyclical oligogyny, that is characterizedby a reduction in queen number from colony initiation to colonyreproduction. We did not find any evidence that one or a fewqueens monopolized egg laying or that there was any inbreeding,both of which have been hypothesized to increase relatednessamong workers. Another factor that can increase relatednessamong workers and the brood they rear is withincolony segregationon the basis of relatedness. We found that combmate pupae aresignificantly more closely related to each other (r = .41) thanthey are to pupae in other combs (r = .33), but we have notinvestigated whether workers take advantage of these relatednesspatterns. This distribution of relatedness among combs willoccur if queens do not lay eggs randomly throughout the nest,but concentrate their egg laying on one or a subset of the availablecombs.     

Olfactory kin recognition in a songbird

The ability to recognize close relatives in order to cooperate or to avoid inbreeding is widespread across all taxa. One accepted mechanism for kin recognition in birds is associative learning of visual or acoustic cues. However, how could individuals ever learn to recognize unfamiliar kin? Here, we provide the first evidence for a novel mechanism of kin recognition in birds. Zebra finch (Taeniopygia guttata) fledglings are able to distinguish between kin and non-kin based on olfactory cues alone. Since olfactory cues are likely to be genetically based, this finding establishes a neglected mechanism of kin recognition in birds, particularly in songbirds, with potentially far-reaching consequences for both kin selection and inbreeding avoidance.     

Darwin's ‘one special difficulty’: celebrating Darwin 200

Darwin identified eusocial evolution, especially of complex insect societies, as a particular challenge to his theory of natural selection. A century later, Hamilton provided a framework for selection on inclusive fitness. Hamilton''s rule is robust and fertile, having generated multiple subdisciplines over the past 45 years. His suggestion that eusociality can be explained via kin selection, however, remains contentious. I review the continuing debate on the role of kin selection in eusocial evolution and suggest some lines of research that should resolve that debate.     

Kin distribution of amphibian larvae in the wild

According to kin selection theory, the location of an individual with respect to its relatives can have important ramifications for its fitness. Perhaps more than any other vertebrate group, anuran amphibian larvae have been the subject of many experiments on this topic. Some anuran species have been shown in the laboratory to recognize and associate with their siblings and half-siblings. However, due to the difficulty of identifying sibships, no kinship studies with anuran larvae have been conducted in the wild. Here, we use microsatellite analysis to show that wood frog (Rana sylvatica) tadpoles were nonrandomly distributed in two ponds with respect to their relatives. In one pond, the tadpoles were significantly clumped with their siblings or half-siblings as expected from other published laboratory studies on this species. However, in another pond, the tadpoles were significantly nonrandomly dispersed from their siblings or half-siblings. This is the first example of kin repulsion of nonreproductive animals in the wild and the first time a species has been shown to display both aggregation and repulsion under different circumstances. These results suggest that kin distribution is context dependent and demonstrate the importance of testing kin selection hypotheses under natural conditions.     

A general model of the public goods dilemma

An individually costly act that benefits all group members is a public good. Natural selection favours individual contribution to public goods only when some benefit to the individual offsets the cost of contribution. Problems of sex ratio, parasite virulence, microbial metabolism, punishment of noncooperators, and nearly all aspects of sociality have been analysed as public goods shaped by kin and group selection. Here, I develop two general aspects of the public goods problem that have received relatively little attention. First, variation in individual resources favours selfish individuals to vary their allocation to public goods. Those individuals better endowed contribute their excess resources to public benefit, whereas those individuals with fewer resources contribute less to the public good. Thus, purely selfish behaviour causes individuals to stratify into upper classes that contribute greatly to public benefit and social cohesion and to lower classes that contribute little to the public good. Second, if group success absolutely requires production of the public good, then the pressure favouring production is relatively high. By contrast, if group success depends weakly on the public good, then the pressure favouring production is relatively weak. Stated in this way, it is obvious that the role of baseline success is important. However, discussions of public goods problems sometimes fail to emphasize this point sufficiently. The models here suggest simple tests for the roles of resource variation and baseline success. Given the widespread importance of public goods, better models and tests would greatly deepen our understanding of many processes in biology and sociality.     

Cooperative bird differentiates between the calls of different individuals, even when vocalizations were from completely unfamiliar individuals

Hypotheses proposed to explain the evolution of cooperative behaviour typically require differentiation between either groups of conspecifics (e.g. kin/non-kin) or, more typically, individuals (e.g. reciprocal altruism). Despite this, the mechanisms that facilitate individual or class recognition have rarely been explored in cooperative species. This study examines the individual differentiation abilities of noisy miners (Manorina melanocephala), a species with one of the most complex avian societies known. Miners permanently occupy colonies numbering into hundreds of individuals. Within these colonies, cooperative coalitions form on a fission-fusion basis across numerous contexts, from social foraging through to mobbing predators. Birds often use individually distinctive 'chur' calls to recruit others to a caller's location, facilitating coalition formation. I used the habituation-discrimination paradigm to test the ability of miners to differentiate between the chur calls of two individuals that were both either: (i) familiar, or (ii) unfamiliar to the focal subject. This technique had not, to my knowledge, been used to assess vocalization differentiation in cooperative birds previously, but here demonstrated that miners could correctly use the spectral features of signals to differentiate between the vocalizations of different individuals, regardless of their familiarity. By attending to individual differences in recruitment calls, miners have a communication system that is capable of accommodating even the most complex cooperative hypotheses based upon acoustic information.