Reply to Kiers et al.: Economic and Biological Clarity in the Theory of Mutualism

Kiers et al. (1) make three main points. First, they noted that many mutualisms involve multiple symbionts interacting with a single host. We agree, and we explained that partner fidelity feedback (PFF) can function because plants generally “limit, withdraw, or even abscise investment in shoots, flowers, and roots (or subsets of any of these) after physical damage or deficits of… resources…” (2). This “modularity” of plant hosts (3) separates the effects of different symbionts and allows the host to react to individual symbionts. Modularity is easily incorporated into our model, because (with no change in our results) principal-agent theory allows the assumption of one agent per host to be replaced …Organismic and Evolutionary Biolog

Non-nest mate discrimination and clonal colony structure in the parthenogenetic ant Cerapachys biroi

Understanding the interplay between cooperation and conflict in social groups is a major goal of biology. One important factor is genetic relatedness, and animal societies are usually composed of related but genetically different individuals, setting the stage for conflicts over reproductive allocation. Recently, however, it has been found that several ant species reproduce predominantly asexually. Although this can potentially give rise to clonal societies, in the few well-studied cases, colonies are often chimeric assemblies of different genotypes, due to worker drifting or colony fusion. In the ant Cerapachys biroi, queens are absent and all individuals reproduce via thelytokous parthenogenesis, making this species an ideal study system of asexual reproduction and its consequences for social dynamics. Here, we show that colonies in our study population on Okinawa, Japan, recognize and effectively discriminate against foreign workers, especially those from unrelated asexual lineages. In accord with this finding, colonies never contained more than a single asexual lineage and average pairwise genetic relatedness within colonies was extremely high (r = 0.99). This implies that the scope for social conflict in C. biroi is limited, with unusually high potential for cooperation and altruis

Phylogeography and genetic diversity of a widespread Old World butterfly, Lampides boeticus (Lepidoptera: Lycaenidae)

<p>Abstract</p> <p>Background</p> <p>Evolutionary genetics provides a rich theoretical framework for empirical studies of phylogeography. Investigations of intraspecific genetic variation can uncover new putative species while allowing inference into the evolutionary origin and history of extant populations. With a distribution on four continents ranging throughout most of the Old World, <it>Lampides boeticus </it>(Lepidoptera: Lycaenidae) is one of the most widely distributed species of butterfly. It is placed in a monotypic genus with no commonly accepted subspecies. Here, we investigate the demographic history and taxonomic status of this widespread species, and screen for the presence or absence of the bacterial endosymbiont <it>Wolbachia</it>.</p> <p>Results</p> <p>We performed phylogenetic, population genetic, and phylogeographic analyses using 1799 bp of mitochondrial sequence data from 57 specimens collected throughout the species' range. Most of the samples (>90%) were nearly genetically identical, with uncorrected pairwise sequence differences of 0 – 0.5% across geographic distances > 9,000 km. However, five samples from central Thailand, Madagascar, northern Australia and the Moluccas formed two divergent clades differing from the majority of samples by uncorrected pairwise distances ranging from 1.79 – 2.21%. Phylogenetic analyses suggest that <it>L. boeticus </it>is almost certainly monophyletic, with all sampled genes coalescing well after the divergence from three closely related taxa included for outgroup comparisons. Analyses of molecular diversity indicate that most <it>L. boeticus </it>individuals in extant populations are descended from one or two relatively recent population bottlenecks.</p> <p>Conclusion</p> <p>The combined analyses suggest a scenario in which the most recent common ancestor of <it>L. boeticus </it>and its sister taxon lived in the African region approximately 7 Mya; extant lineages of <it>L. boeticus </it>began spreading throughout the Old World at least 1.5 Mya. More recently, expansion after population bottlenecks approximately 1.4 Mya seem to have displaced most of the ancestral polymorphism throughout its range, though at least two early-branching lineages still persist. One of these lineages, in northern Australia and the Moluccas, may have experienced accelerated differentiation due to infection with the bacterial endosymbiont <it>Wolbachia</it>, which affects reproduction. Examination of a haplotype network suggests that Australia has been colonized by the species several times. While there is little evidence for the existence of morphologically cryptic species, these results suggest a complex history affected by repeated dispersal events.</p

A Social Parasite Evolved Reproductive Isolation from Its Fungus-Growing Ant Host in Sympatry

SummaryInquiline social parasitic ant species exploit colonies of other ant species mainly by producing sexual offspring that are raised by the host. Ant social parasites and their hosts are often close relatives (Emery’s rule), and two main hypotheses compete to explain the parasites’ evolutionary origins: (1) the interspecific hypothesis proposes an allopatric speciation scenario for the parasite, whereas (2) the intraspecific hypothesis postulates that the parasite evolves directly from its host in sympatry [1–10]. Evidence in support of the intraspecific hypothesis has been accumulating for ants [3, 5, 7, 9–12], but sympatric speciation remains controversial as a general speciation mechanism for inquiline parasites. Here we use molecular phylogenetics to assess whether the socially parasitic fungus-growing ant Mycocepurus castrator speciated from its host Mycocepurus goeldii in sympatry. Based on differing patterns of relationship in mitochondrial and individual nuclear genes, we conclude that host and parasite occupy a temporal window in which lineage sorting has taken place in the mitochondrial genes but not yet in the nuclear alleles. We infer that the host originated first and that the parasite originated subsequently from a subset of the host species’ populations, providing empirical support for the hypothesis that inquiline parasites can evolve reproductive isolation while living sympatrically with their hosts

Characterization and Comparison of Convergence Among \u3cem\u3eCephalotus follicularis\u3c/em\u3e Pitcher Plant-Associated Communities with Those of \u3cem\u3eNepenthes\u3c/em\u3e and \u3cem\u3eSarracenia\u3c/em\u3e Found Worldwide

The Albany pitcher plant, Cephalotus follicularis, has evolved cup-shaped leaves and a carnivorous habit completely independently from other lineages of pitcher plants. It is the only species in the family Cephalotaceae and is restricted to a small region of Western Australia. Here, we used metabarcoding to characterize the bacterial and eukaryotic communities living in C. follicularis pitchers at two different sites. Bacterial and eukaryotic communities were correlated in both richness and composition; however, the factors associated with richness were not the same across bacteria and eukaryotes, with bacterial richness differing with fluid color, and eukaryotic richness differing with the concentration of DNA extracted from the fluid, a measure roughly related to biomass. For turnover in composition, the variation in both bacterial and eukaryotic communities primarily differed with fluid acidity, fluid color, and sampling site. We compared C. follicularis-associated community diversity with that of Australian Nepenthes mirabilis, as well as a global comparison of Southeast Asian Nepenthes and North American Sarracenia. Our results showed similarity in richness with communities from other pitcher plants, and specific bacterial taxa shared among all three independent lineages of pitcher plants. Overall, we saw convergence in richness and particular clades colonizing pitcher plants around the world, suggesting that these highly specialized habitats select for certain numbers and types of inhabitants

The Direct and Ecological Costs of an Ant-Plant Symbiosis

How strong is selection for cheating in mutualisms? The answer depends on the type and magnitude of the costs of the mutualism. Here we investigated the direct and ecological costs of plant defense by ants in the association between Cordia nodosa, a myrmecophytic plant, and Allomerus octoarticulatus, a phytoecious ant. Cordia nodosa trees produce food and housing to reward ants that protect them against herbivores. For nearly 1 year, we manipulated the presence of A. octoarticulatus ants and most insect herbivores on C. nodosa in a full-factorial experiment. Ants increased plant growth when herbivores were present but decreased plant growth when herbivores were absent, indicating that hosting ants can be costly to plants. However, we did not detect a cost to ant colonies of defending host plants against herbivores. Although this asymmetry in costs suggests that the plants may be under stronger selection than the ants to cheat by withholding investment in their partner, the costs to C. nodosa are probably at least partly ecological, arising because ants tend scale insects on their host plants. We argue that ecological costs should favor resistance or traits other than cheating and thus that neither partner may face much temptation to cheat.Organismic and Evolutionary Biolog

Development of the method for estimating muscle-length change by means of bio-electrical impedance method

博士論文要

Are Mutualisms Maintained by Host Sanctions or Partner Fidelity Feedback?

Although mutualisms are common in all ecological communities and have played key roles in the diversification of life, our current understanding of the evolution of cooperation applies mostly to social behavior within a species. A central question is whether mutualisms persist because hosts have evolved costly punishment of cheaters. Here, we use the economic theory of employment contracts to formulate and distinguish between two mechanisms that have been proposed to prevent cheating in host-symbiont mutualisms, Partner Fidelity Feedback (PFF) and Host Sanctions (HS). Under PFF, positive feedback between host fitness and symbiont fitness is sufficient to prevent cheating; in contrast, HS posits the necessity of costly punishment to maintain mutualism. A coevolutionary model of mutualism finds that HS are unlikely to evolve de novo, and published data on legume-rhizobia and yucca-moth mutualisms are consistent with PFF and not HS. Thus, in systems considered to be textbook cases of HS, we find poor support for the theory that hosts have evolved to punish cheating symbionts; instead, we show that even horizontally transmitted mutualisms can be stabilized via PFF. PFF theory may place previously underappreciated constraints on the evolution of mutualism, and explain why punishment is far from ubiquitous in nature.EconomicsOrganismic and Evolutionary Biolog

The draft genome of a socially polymorphic halictid bee, Lasioglossum albipes

Background: Taxa that harbor natural phenotypic variation are ideal for ecological genomic approaches aimed at understanding how the interplay between genetic and environmental factors can lead to the evolution of complex traits. Lasioglossum albipes is a polymorphic halictid bee that expresses variation in social behavior among populations, and common-garden experiments have suggested that this variation is likely to have a genetic component. Results: We present the L. albipes genome assembly to characterize the genetic and ecological factors associated with the evolution of social behavior. The de novo assembly is comparable to other published social insect genomes, with an N50 scaffold length of 602 kb. Gene families unique to L. albipes are associated with integrin-mediated signaling and DNA-binding domains, and several appear to be expanded in this species, including the glutathione-s-transferases and the inositol monophosphatases. L. albipes has an intact DNA methylation system, and in silico analyses suggest that methylation occurs primarily in exons. Comparisons to other insect genomes indicate that genes associated with metabolism and nucleotide binding undergo accelerated evolution in the halictid lineage. Whole-genome resequencing data from one solitary and one social L. albipes female identify six genes that appear to be rapidly diverging between social forms, including a putative odorant receptor and a cuticular protein. Conclusions: L. albipes represents a novel genetic model system for understanding the evolution of social behavior. It represents the first published genome sequence of a primitively social insect, thereby facilitating comparative genomic studies across the Hymenoptera as a whole