Sociality and kin selection in insects 鄭先祐 (Ayo) 國立台南大學 環境生態研究所

kin selection in insects2 Contents 9.1 introduction 9.2 The origin and evolution of eu-sociality ( 真社會性 ) 9.3 The evolution of a stable reproductive skew 9.4 Sex ratio evolution and kin conflict in social insects 9.5 conclusion

kin selection in insects3 9.1 Introduction Eusocial society( 真社會性的社會 ): alongside cooperative care of the brood and an overlap of adult generations, exhibit a reproductive division of labour ( 生殖工作的分工 ). Some members are specialized for reproduction (queens or kings), whereas others devote themselves to foraging, nest construction, defence and brood-reaing. Reproductive altruism ( 生殖的利他性 )

kin selection in insects4 Eusocial insects Most eusocial insects belong to two orders, the Hymenoptera ( 膜翅目 ) (ants, bees and wasps) and the Isoptera (termites) ( 白蟻 ). All ants and termites are eusocial, but many bees and wasps are solitary or exhibit other grades of social organization. A number of aphids (Hemiptera) are arguably also eusocial, as are some beetles and thrips. Table 9.1 The major groups of eusocial insects and their traits.

kin selection in insects5 Hamilton’s rule Hamilton’s theory of kin selection. the evolution of altruism and sociality Hamilton’s rule, the gene for altruism undergoes selection if the condition r1b - r2c > 0 is satisfied. r1 is the altruist’s relatedness to the beneficiary’s offspring ( 有利於子代 ) x b( 增加數 ) r2 is the altruist’s relatedness to its own offspring. ( 對自己子代的犧牲 ) x c ( 減少數 )

kin selection in insects6 West-Eberhard (1975), 將 Hamilton’s rule 轉 換為 if rb – c > 0, where r is the relatedness of the altruist to the beneficiary. Table 9.2 Relatedness levels in a social insect colony.

kin selection in insects7 9.2 The origin and evolution of eusociality The necessity of kin selection Hymenopteran eusociality and the haplodiploidy( 單套雙套 ) hypothesis The origin of eusociality in the termites

kin selection in insects8 The necessity of kin selection Reciprocal altruism( 相互利他 ) is not ‘true’ altruism. Eusociality usually entails true altruism ( 真正 的利他 ). Hamilton’s rule shows that both genetic factors (affecting relatedness) and ecological ones (affecting benefit and cost) must be important in promoting eusocial evolution. Eusocial evolution : Mutualism hypothesis vs. parental manipulation hypothesis

kin selection in insects9 Hymenopteran eusociality and the haplodiploidy hypothesis Eusociality has evolved independently many times among the insects. Wilson (1971) estimated that there have been 11 origins of eusociality in the Hymenoptera, and one in the termites. A phylogeny based on mitochondrial DNA sequences suggests that the aphid family Hormaphididae evolved a a soldier caste at least five times.

kin selection in insects10 Relatedness levels in the Hymenoptera Males are haploid and develop from unfertilized eggs, but females are diploid and develop from fertilized eggs. (haplo-diploidy) 如此，整體 的 relatedness 比較高。 Haplo-diploidy hypothesis

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kin selection in insects The evolution of a stable reproductive skew Skew theory suggest several factors of this type. Fig. 9.2 factors affect the stable level of reproductive skew. 促進 reproductive skew 的因素： Group productivity, ecological constraints, relatedness 抑制的因素： subordinate fighting ability

kin selection in insects13 Skew evolution in the polistine wasps Reeve and Nonacs (1992) Polistes fuscatus wasps, skew reproduction, 有多個雌蜂， alpha, beta 偷偷移走一些 eggs Alpha queens showed no consistent response to egg removal, but beta ones became more aggressive on average.

kin selection in insects14 Skew evolution in the leptothoracine ants Bourke and Heinze (1994), polygynous colonies live in extended uniform habitats such as pinewoods. Cost of dispersal are therefore relatively low. All queens lay eggs and live together peaceably. (skew is low) Monogynous colonies live in a rocky area. Cost of dispersal is high. Permanently wingless, only one queen.

kin selection in insects Sex ratio evolution and kin conflict in social insects Relatedness asymmetry = relateness to systers / relatedness to brothers 0.75/0.25 = 3:1 (Table 9.2) Sex ratio = 3:1 in favour of females. Tests of sex ratio theory in social Hymenoptera Table 9.4 Tests of sex ratio theory within monogynous, non-parasitic ant species. Population sex investment ratio 通常都是偏向雌性 (>0.5) ， 唯一有個例外 (0.36)

kin selection in insects16 Some colonies at mother-daughter associations should produce female-biased broods. Sundstrom (1994), monogynous population of wood ant (Formica truncorum), using allozyme analysis. Some colonies had a multiply mated queen, produced mostly males Others had a singly mated queen produced mainly females.

kin selection in insects17 How workers manipulate sex allocation Sundstrom et al. (1996) shown that all queens in a monogynous population of Formica exsecta contributed a similar fraction of haploid eggs to their colony’s egg pool. However, workers in colonies headed by singly mated queens raised a female bias of adult sexuals, Whereas workers under multiply mated queens raised a male bias.

kin selection in insects conclusion Two unsolved issues: 1. The adaptive significance of within-colony kin discrimination 2. The evolution of multiple mating.

kin selection in insects19 問題與討論