Masakado Kawata

A worldwide survey of genome sequence variation provides insight into the evolutionary history of the honeybee Apis mellifera.

The honeybee Apis mellifera has major ecological and economic importance. We analyze patterns of genetic variation at 8.3 million SNPs, identified by sequencing 140 honeybee genomes from a worldwide sample of 14 populations at a combined total depth of 634×. These data provide insight into the evolutionary history and genetic basis of local adaptation in this species. We find evidence that population sizes have fluctuated greatly, mirroring historical fluctuations in climate, although contemporary populations have high genetic diversity, indicating the absence of domestication bottlenecks. Levels of genetic variation are strongly shaped by natural selection and are highly correlated with patterns of gene expression and DNA methylation. We identify genomic signatures of local adaptation, which are enriched in genes expressed in workers and in immune system– and sperm motility–related genes that might underlie geographic variation in reproduction, dispersal and disease resistance. This study provides a framework for future investigations into responses to pathogens and climate change in honeybees.

Why is adaptation prevented at ecological margins? New insights from individual‐based simulations

All species are restricted in their distribution. Currently, ecological models can only explain such limits if patches vary in quality, leading to asymmetrical dispersal, or if genetic variation is too low at the margins for adaptation. However, population genetic models suggest that the increase in genetic variance resulting from dispersal should allow adaptation to almost any ecological gradient. Clearly therefore, these models miss something that prevents evolution in natural populations. We developed an individual-based simulation to explore stochastic effects in these models. At high carrying capacities, our simulations largely agree with deterministic predictions. However, when carrying capacity is low, the population fails to establish for a wide range of parameter values where adaptation was expected from previous models. Stochastic or transient effects appear critical around the boundaries in parameter space between simulation behaviours. Dispersal, gradient steepness, and population density emerge as key factors determining adaptation on an ecological gradient.

The evolution of extreme shell shape variation in the land snail Ainohelix editha: a phylogeny and hybrid zone analysis

Ainohelix editha from Hokkaido, Japan, exhibit great geographical variation in their shell morphology. In particular, A. editha in two quite separate locations, Shimamaki and Samani, are striking because they are extremely flat and have a sharp keel, whereas at adjacent sites the shells are globular or depressed‐globular. We used mitochondrial 16S rRNA and nuclear ITS‐2 sequences to infer a phylogeny among 47 snails from 29 locations. Snails from the two keeled‐flat populations clustered separately in the phylogeny, suggesting that this unusual shell form could have evolved independently. A morphological analysis of shells collected along a transect between keeled‐flat and globular snail sites showed a cline for shell shape and the angle of the keel. Two different mtDNA lineages were found across the transect, with a cline for an ITS‐2 single nucleotide polymorphism. Together, the results may suggest a lack of reproductive isolation between keeled‐flat and globular snails, with possible introgression by hybridization.

Fluctuating populations and kin interaction in mammals.

Kin selection in animals favors less aggressive interaction among related individuals. If the genetic relatedness among neighbors changes with population structure and density, behavioral interaction may also change according to the population structure. Charnov and Finerty proposed a hypothesis that kin selection in voles causes population cycles if the relatedness among neighbors decreases as density increases. Field experiments have recently tested this hypothesis. Furthermore, field studies of social interaction in voles have increased in number, so that the effects of kinship on reproductive success can be reviewed. These studies indicate that although kin interaction might be an important factor affecting social behavior and reproductive success in voles, the relationships both between kinship and degree of amicable behavior or reproductive rate, and between relatedness among neighbors and population density, are far less simple than had been supposed.

Frpm artificial individuals to global patterns

Artificial Life is a model of biological systems that describes lives archived by computer simulation, chemical substrates or any other non-biological substrates. Artificial Life simulation adopts a bottom-up approach in which behavior of lower-level entities (e.g. molecules, cells and individuals) is all that is programed; global patterns (e.g. evolutionary patterns observed at the level of the population and the community) can emerge as a result of interaction among lower-level entities. Artificial Life simulations will be used not only to test ecological and evolutionary hypotheses explaining real organisms but also to show the validity of general theories, processes and concepts such as natural selection, theories of complexity, hierarchical relations and self-organization.

A new hypothesis for species coexistence: male–male repulsion promotes coexistence of competing species

We propose a new hypothesis for species coexistence by considering behavioral interactions between individuals. The hypothesis states that repulsive behavior between conspecific males (male–male repulsion) creates space for competing species, which promotes their coexistence. This hypothesis can explain the coexistence of two competing species even when their ecological niches completely overlap in spatially homogeneous environments. In addition, the mechanisms underlying such behavior might play a role in enabling the coexistence of two species immediately after speciation, with little or no niche differentiation, as in the case of cichlid fish communities, for example. Although there is limited evidence supporting this hypothesis, it can nevertheless explain the occurrence of species coexistence and biodiversity, which cannot be explained by previous theories.

Mating system and reproductive success in a spring population of the red-backed vole, Clethrionomys rufocanus bedfordiae

The mating system of the red-backed vole, Clethrionomys rufocanus bedfordiae (Thomas), was examined in a wind shelter-belt and in the laboratory by using markrecapture and electrophoretic techniques. (1) Most of the adult females copulated at post-partum estrus. Birth synchrony was observed in both the field and laboratory. (2) The females occupied exclusive home ranges, while the males usually had overlapping home ranges that often enclosed those of several females. (3) The estimation of frequency of multiple paternity indicated that multiple paternity was rare in this population. (4) The paternity of twelve litters were determined. No male whose home range did not overlap with a females range sired any of her offspring. However, the degree of the overlap did not always affect copulatory success. No male successfully copulated with two females who had synchronized their parturitions (4 cases). (5) The body weight, testis weight, seminal vesicle weight, adrenal gland weight, flank gland size, and root ratio (age) of 10 successful males were compared with those of all captured adult males. Strong evidence for mate selection in these six male traits could not be found, although some differences in the means of flank gland size and seminal vesicle weight between 10 successful males and the population were observed.

A genetically explicit model of speciation by sensory drive within a continuous population in aquatic environments

BackgroundThe sensory drive hypothesis predicts that divergent sensory adaptation in different habitats may lead to premating isolation upon secondary contact of populations. Speciation by sensory drive has traditionally been treated as a special case of speciation as a byproduct of adaptation to divergent environments in geographically isolated populations. However, if habitats are heterogeneous, local adaptation in the sensory systems may cause the emergence of reproductively isolated species from a single unstructured population. In polychromatic fishes, visual sensitivity might become adapted to local ambient light regimes and the sensitivity might influence female preferences for male nuptial color. In this paper, we investigate the possibility of speciation by sensory drive as a byproduct of divergent visual adaptation within a single initially unstructured population. We use models based on explicit genetic mechanisms for color vision and nuptial coloration.ResultsWe show that in simulations in which the adaptive evolution of visual pigments and color perception are explicitly modeled, sensory drive can promote speciation along a short selection gradient within a continuous habitat and population. We assumed that color perception evolves to adapt to the modal light environment that individuals experience and that females prefer to mate with males whose nuptial color they are most sensitive to. In our simulations color perception depends on the absorption spectra of an individuals visual pigments. Speciation occurred most frequently when the steepness of the environmental light gradient was intermediate and dispersal distance of offspring was relatively small. In addition, our results predict that mutations that cause large shifts in the wavelength of peak absorption promote speciation, whereas we did not observe speciation when peak absorption evolved by stepwise mutations with small effect.ConclusionThe results suggest that speciation can occur where environmental gradients create divergent selection on sensory modalities that are used in mate choice. Evidence for such gradients exists from several animal groups, and from freshwater and marine fishes in particular. The probability of speciation in a continuous population under such conditions may then critically depend on the genetic architecture of perceptual adaptation and female mate choice.

Invasion of vacant niches and subsequent sympatric speciation

An individual-based simulation study was conducted to examine the population dynamics of ‘invasion of a vacant niche’ and subsequent speciation (by reproductive isolation) when food resources are randomly distributed spatially within the habitat and the frequencies of different food types are bimodally distributed (i.e. smaller and larger sizes of food being most abundant). The initially vacant niche was that of unused larger sizes of food. When phenotypic variation for resource use (i.e. food sizes) was small in the initial population, and each female could choose a mate from anywhere in the habitat, the population could not invade the vacant niche. But when the dispersal distance of the offspring and the area within which a female could choose a mate were small (i.e. the genetic neighbourhood size was small), the population could, in most cases, evolve to use both smaller and larger food sizes and form sister species sympatrically, with each species utilizing one of the two niches (small and large sizes of food). When phenotypic variation in resource use in the initial population was large, the population could, in most cases, invade the vacant niche by evolving to use both smaller and larger sizes of food. The probability of speciation increased as the dispersal distance of offspring decreased. The results indicate that populations whose individuals have small Wrights genetic neighbourhoods may often exploit a vacant niche and diversify sympatrically in the process.

Pregnancy failure and suppression by female-female interaction in enclosed populations of the red-backed vole,Clethrionomys rufocanus bedfordiae

SummaryExperimental populations of the redbacked vole,Clethrionomys rufocanus bedfordiae (Thomas), were introduced into field enclosures and then subsequently checked for home range overlap and reproductive condition. The times to parturition of females that did not have exclusive home ranges were significantly delayed compared with those of females whose ranges did not overlap (Table 4). The delays in parturition were not significantly related to the age of the females or to the number and ages of males that overlapped with a female. Copulatory plugs observed in the females that did not have exclusive ranges indicated that they often failed to become pregnant, regardless of having copulated. After the acquisition of exclusive ranges, these same females came into estrus and became pregnant (Figs. 2, 3).