A Test of the Mating Limitation Hypothesis for Caste Determination in Evylaeus albipes (Hymenoptera: Halictidae), a Primitively Eusocial Halictine Bee

Yanega's (1997) mating limitation hypothesis (MLH) states that if a female mates promptly after emerging, she then becomes a member of the maximally reproductive behavioral caste (i.e., in most cases an overwintering gyne). Females that do not mate early become workers. We tested the MLH in laboratory colonies of a eusocial population of Evylaeus albipes. Of 24 worker brood females (13 from queenright and 11 from orphaned nests), 13 mated on the first day of flight activity and all mated within the first 5 days; there were no significant differences between mating rates of females from the two colony types. All 24 commenced foraging as workers after an average of between 3 and 4 days postmating. We conclude that the MLH does not apply to this species despite the fact that the only known halictine for which this hypothesis has been experimentally tested is the fairly closely related E. marginatus.     

The sight of the peacock’s tail makes me sick: The early arguments on sexual selection

Why does a peacock have a beautiful train, while a peahen is sober without such flamboyance? Darwin proposed the theory of sexual selection to explain the differences between the sexes of the same species. Recently the study of sexual selection has been one of the most flourishing areas in evolutionary biology. However, the theory met with great resistance from biologists since the publication of the idea and the history of the theory included a lot of misunderstanding and confusion. There are several reasons for this. First, classical Darwinism failed to recognize social competition as an important selective force. Second, the good-for-the-species argument, which persisted in the days after Darwin, made the sexual selection argument more difficult to understand. Compared to the discussions on animals, Darwin’s argument on human sex differences is not satisfactory. The reason probably lies in the debate over human racial differences which prevailed in the 19th century.     

Genetic caste determination in Pogonomyrmex harvester ants imposes costs during colony founding

Some populations of Pogonomyrmex harvester ants comprise genetically differentiated pairs of interbreeding lineages. Queens mate with males of their own and of the alternate lineage and produce pure-lineage offspring which develop into queens and inter-lineage offspring which develop into workers. Here we tested whether such genetic caste determination is associated with costs in terms of the ability to optimally allocate resources to the production of queens and workers. During the stage of colony founding, when only workers are produced, queens laid a high proportion of pure-lineage eggs but the large majority of these eggs failed to develop. As a consequence, the number of offspring produced by incipient colonies decreased linearly with the proportion of pure-lineage eggs laid by queens. Moreover, queens of the lineage most commonly represented in a given mating flight produced more pure-lineage eggs, in line with the view that they mate randomly with the two types of males and indiscriminately use their sperm. Altogether these results predict frequency-dependent selection on pairs of lineages because queens of the more common lineage will produce more pure-lineage eggs and their colonies be less successful during the stage of colony founding, which may be an important force maintaining the coexistence of pairs of lineages within populations.     

Fertilization competence and sperm size variation in sperm-heteromorphic insects

Between species, variation in sperm size has been related to male–female coevolution and male–male competition. In contrast, variation within species is poorly understood. A particular case of intraspecific sperm-size variation occurs in sperm-heteromorphic species, where males produce distinct sperm morphotypes, usually only one of which is fertile. This allows to investigate sperm size variation under different selection regimes. Nonfertile morphotypes, whose role is aside from fertilization, may have other functions, and this may be reflected by changes in developmental processes and a different phenotype compared to fertile sperm. We show that the intraspecific coefficient of variation in sperm length is up to four times lower for fertile than nonfertile morphotypes across 150 sperm-heteromorphic species (70 butterfly, 71 moth, 9 diopsid fly species). This is in agreement with a previous study on 11 species in the Drosophila obscura group. Significantly lower variation in fertile than nonfertile sperm morphometry may result from fertilization-related selection for optimal sperm size, novel functions of nonfertile sperm, or from tighter control of fertile sperm development. More data are needed to clarify the consequences and adaptive significance of within-morph variation, and its consistent pattern across sperm-heteromorphic insects.Co-ordinating editor: Hurst     

The Philosophy of Donald T. Campbell: A Short Review and Critical Appraisal

Aside from his remarkable studies in psychology and the social sciences, Donald Thomas Campbell (1916–1996) made significant contributions to philosophy, particularly philosophy of science,epistemology, and ethics. His name and his work are inseparably linked with the evolutionary approach to explaining human knowledge (evolutionary epistemology). He was an indefatigable supporter of the naturalistic turn in philosophy and has strongly influenced the discussion of moral issues (evolutionary ethics). The aim of this paper is to briefly characterize Campbells work and to discuss its philosophical implications. In particular, I show its relevance to some current debates in the intersection of biology and philosophy. In fact, philosophy of biology would look poorer without Campbells influence. The present paper is not a hagiography but an attempt to evaluate and critically discuss the meaning of Campbells work for philosophy of biology and to encourage scholars working in this field to read and re-read this work which is both challenging and inspiring.     

Michael Ruse and His Fifteen Years of Booknotes – For Better or for Worse

In this paper I trace Michael Ruse's Booknotes from the first volumeof Biology and Philosophy in 1986 to the present. I deal withboth the style and the content of these booknotes. Ruse paid specialattention to authors outside of the traditional English axis as wellas to feminist writers. He complained that too much attention wasbeing paid to certain topics (e.g., evolutionary ethics, evolutionaryepistemology, the species problem and reduction) while other, moreimportant topics were all but ignored (e.g., natural selection,population genetics, levels of selection and extraterrestrial life).He also dealt with the Darwin Industry. Creationism, his love-haterelationships with several authors and his undiluted love of CharlesDickens.     

对蜜蜂性别决定和蜂王级型确立理论的新诠释

从全新视角概貌性解读蜜蜂Apis诸多生殖机制,依据的就是蜂王或产卵工蜂的卵子发生、性别决定假说、性位点研究以及蜂王级型确立机制。这种不同于单倍-二倍性性别决定机制的新诠释,适用于明确性别决定机制、简化定向育种方法、减少比较性实验的难度和时间、实施亲子鉴定和抽象并量化种群的概念。     

Random sperm use and genetic effects on worker caste fate in Atta colombica leaf-cutting ants

Sperm competition can produce fascinating adaptations with far-reaching evolutionary consequences. Social taxa make particularly interesting models, because the outcome of sexual selection determines the genetic composition of groups, with attendant sociobiological consequences. Here, we use molecular tools to uncover some of the mechanisms and consequences of sperm competition in the leaf-cutting ant Atta colombica, a species with extreme worker size polymorphism. Competitive PCR allowed quantification of the relative numbers of sperm stored by queens from different males, and offspring genotyping revealed how sperm number translated into paternity of eggs and adult workers. We demonstrate that fertilization success is directly related to sperm numbers, that stored sperm are well-mixed and that egg paternity is constant over time. Moreover, worker size was found to have a considerable genetic component, despite expectations that genetic effects on caste fate should be minor in species with a low degree of polyandry. Our data suggest that sexual conflict over paternity is largely resolved by the lifetime commitment between mates generated by long-term sperm storage, and show that genetic variation for caste can persist in societies with comparatively high relatedness.     

Extensive evolutionary rate variation in floral color determining genes in the genus Ipomoea

Flower color is an important adaptive trait in many plant species because it determines reproductive success through differential attractiveness to insect pollinators. The genus Ipomoea is a pan tropically distributed plant genus characterized by showy flowers that often differ in color among closely related species. Flower color is determined primarily by products of the anthocyanin biosynthesis pathway. To determine whether flower color evolution among members of the genus is driven by adaptive molecular evolution of the anthocyanin pathway genes, we analyzed data from 10 genes sequenced from 19 species of Ipomoea . Six protein-coding genes from the anthocyanin pathway were drawn for evolutionary analysis in addition to three genes from the unrelated leucine biosynthesis pathway and one MADS box regulatory gene for comparison. The analyses provided: (i) no convincing evidence for positive selection on anthocyanin pathway structural genes, or on the other sampled genes, despite shifts in flower color among species included in the sample; (ii) pathway position correlated weakly with estimates of the intensity of evolutionary constraint on the anthocyanin pathway enzyme coding genes; and (iii) there was substantial gene-specific heterogeneity in the rates of synonymous site evolution. Synonymous rate heterogeneity does not appear to be accounted for by codon bias or local contextual or compositional sequence differences, leading us to implicate heterogeneous rates of mutation among genes as the most probable cause of synonymous rate heterogeneity.