Population divergence of aggregation pheromone responses in Ips subelongatus in northeastern China

The Asian larch bark beetle, Ips subelongatus, is considered to be the major pest of larch within its natural range. We investigated the electrophysiological and behavioral characteristics as well as mitochondrial DNA cytochrome oxidase subunit I sequences of L subelongatus from 13 geographic populations throughout northeastern China in order to explore population divergence of aggregation pheromone responses and the extent of potential genetic divergence. Electrophysiological analyses showed that antennae of I. sube-longatus from all the six tested populations responded strongly to （S）-（-）-ipsenol （100% detection; 0.35-0.73 mV） in gas chromatography （GC）-electroantennographic detection （EAD） analyses, while its antipode, （R）-（＋）-ipsenol was antennally inactive. I. subelon- gatus populations varied in their responses to （R）-（-）- and （S）-（＋）-ipsdienol in GC-EAD analyses. Behavioral bioassays demonstrated that （S）-（-）-ipsenol alone was significantly attractive at all the tested sites, supporting its status as a key pheromone component of L subelongatus, whereas （S）-（＋）-ipsdienol was inactive alone. Adding （S）-（＋）-ipsdienol to （S）-（-）-ipsenol did not have any effect on the trap catches from some populations in Inner Mongolia. However, （S）-（＋）-ipsdienol showed a strong synergistic effect on （S）-（-）- ipsenol from several populations in Jilin and Liaoning Provinces, and a weak synergistic effect from some transition populations in Heilongjiang Province. Furthermore, 27 mito- chondrial haplotypes were found among the 13 populations （intraspecific nucleotide di- vergence, 0.1%-1.1%）. Analyses of molecular variance and haplotype networks indicated that different geographic populations have developed some genetic variation but did not form completely independent groups. From an applied point of view, a universal synthetic binary blend ofracemic ipsenol and （S）-（＋）-ipsdienol might have a potential for monitoring or even mass-trapping of I. subelongatus across northeastern China, even though some populations only use （S）-（-）-ipsenol alone as their active pheromone component.

Reinforcement as an initiator of population Jivergence and speciation

When hybridization results in reduced fitness, natural selection is expected to favor the evolution of traits that minimize the likelihood of hybridizing in the first place. This process, termed reinforcement （or, more generally, reproductive character displacement）, thereby contributes to the evolution of enhanced reproductive isolation between hybridizing groups. By enhancing reproductive isolation in this way, reinforcement plays an important role in the final stages of speciation. However, reinforcement can also contribute to the early stages of speciation. Specifically, because selection to avoid hybridization occurs only in sympatric populations, the unfolding of reinforcement can lead to the evolution of traits in sympatric populations that reduce reproduction between conspecifics in sympatry versus those in allopatry. Thus, reinforcement between species can lead to reproductive isolation--and possibly speciation-between populations in sympatry versus those in allopatry or among different sympatric populations. Here, I describe how this process can occur, the conditions under which it is most likely to occur, and the empirical data needed to evaluate the hypothesis that reinforcement can initiate speciation.

The role of male contest competition over mates in speciation

Research on the role of sexual selection in the speciation process largely focuses on the diversifying role of mate choice. In particular, much attention has been drawn to the fact that population divergence in mate choice and in the male traits subject to choice directly can lead to assortative mating. However, male contest competition over mates also constitutes an important mechanism of sexual selection. We review recent empirical studies and argue that sexual selection through male contest competition can affect speciation in ways other than mate choice. For example, biases in aggression towards similar competitors can lead to disruptive and negative frequency-dependent selection on the traits used in contest competition in a similar way as competition for other types of limited resources. Moreover, male contest abilities often trade-off against other abilities such as parasite resistance, protection against predators and general stress tolerance. Populations experiencing different ecological condi- tions should therefore quickly diverge non-randomly in a number of traits including male contest abilities. In resource based breeding systems, a feedback loop between competitive ability and habitat use may lead to further population divergence. We discuss how population divergence in traits used in male contest competition can lead to the build up of reproductive isolation through a number of different pathways. Our main conclusion is that the role of male contest competition in speciation remains largely scientifically unexplored [Current Zoology 58 （3）： 493-509, 2012].

Fitness traits and underlying genetic variation related to host plant specialization in the aphid Sitobion avenae

Sitobion avenae （E） is an important cereal pest worldwide that can survive on various plants in the Poaceae, but divergent selection on different host plants shouldpromote the evolution of specialized genotypes or host races. In order to evaluate their resource use strategies, clones of S. avenae were collected from oat and barley. Host-transfer experiments for these clones were conducted in the laboratory to compare their fitness traits. Our results demonstrated that barley clones had significantly lower fecundityand tended to have longer developmental times when transferred from barley to oat. However, oat clones developed faster after they were transferred to barley. Clones fromoat and barley had diverged to a certain extent in terms of fecundity and developmental time of the nymphs. The separation of barley clones and oat clones of S. avenae was alsoevident in a principal component analysis. Barley clones tended to have higher broad-sense heritabilities for fitness traits than oat clones, indicating the genetic basis of differentiationbetween them. Barley clones showed significantly higher extent of specialization compared to oat clones from two measures of specialization （i.e., Xsp and Ysp）. Therefore, barleyclones were specialized to a certain extent, but oat clones appeared to be generalized. The fitness of S. avenae clones tended to increase with higher extent of specialization. Theevolution toward ecological specialization in S. avenae clones, as well as the underlying genetic basis, was discussed.

Is intraspecific variation in diet and morphology related to environmental gradients?Exploring Liem’s paradox in a cichlid fish

Interspecific studies have demonstrated that trophic morphology and ecology are not always tightly matched:a phenomenon rarely reported at the intraspecific level.In the present study,we explored relationships among diet,morphology and the environment in a widespread cichlid fish,Astatoreochromis alluaudi(Pellegrin 1904),from 6 sites in southern Uganda to test for evidence of eco-morphological matching at the interdemic level.Previous studies of Astatoreochromis alluaudi have demonstrated developmental plasticity in trophic morphology in response to diet:a mollusk diet produces specimens with large pharyngeal jaws and muscles,whereas a soft-food diet produces smaller pharyngeal jaws and corresponding changes in musculature.Sites were chosen to maximize variability in environmental variables that might directly or indirectly affect trophic morphology.We found significant differences in pharyngeal jaw and muscle morphology among populations.Similarly,we found differences in diets among sites:mollusks were found in the stomachs of fish from only 2 populations sampled,despite the presence of mollusks in 5 of the 6 sites.Although trophic morphology did match the observed diet in 2 sites,diet did not correlate with either morphology or environmental variables across sites,nor were environmental variables correlated with morphological variation among sites.These results suggest that mismatch can occur among different populations of a single species for reasons such as seasonality in resources,developmental plasticity and/or complex indirect interactions.Intraspecific mechanisms should be further studied in order to better understand the complex relationships between morphological specialization and ecological generalization.

Genetic variation and cryptic lineage diversity of the Nigerian red-headed rock agama Agama agama associate with eco-geographic zones

Nigeria is an Afrotropical region with considerable ecological heterogeneity and levels of biotic endemism.Among its vertebrate fauna,reptiles have broad distributions,thus,they constitute a compelling system for assessing the impact of ecological variation and geographic isolation on species diversification.The red-headed rock agama,Agama agama,lives in a wide range of habitats and,thus,it may show genetic structuring and diversification.Herein,we tested the hypothesis that ecology affects its genetic structure and population divergence.Bayesian inference phylogenetic analysis of a mitochondrial DNA(mtDNA)gene recovered four well-supported matrilines with strong evidence of genetic structuring consistent with eco-geographic regions.Genetic differences among populations based on the mtDNA also correlated with geographic distance. The ecologicalniche model for the matrilines had a good fit and robust performance. Population divergence alongthe environmental axes was associated with climatic conditions, and temperature ranked highestamong all environmental variables for forest specialists, while precipitation ranked highest for theforest/derived savanna, and savanna specialists. Our results cannot reject the hypothesis that nicheconservatism promotes geographic isolation of the western populations of Nigerian A. agama.Thus, ecological gradients and geographic isolation impact the genetic structure and population divergenceof the lizards. This species might be facing threats due to recent habitat fragmentation,especially in western Nigeria. Conservation actions appear necessary.

Impacts of oxygen deficiency on embryo life-history traits of migratory locust Locusta migratoria from low and high altitudes

Hypoxia challenges aerobic organisms in numerous environments,and hypoxic conditions may become more severe under future climate-change scenarios.The impact of hypoxia on the development of terrestrial insect embryos is not well understood.Here,to address this gap,embryonic life-history traits of migratory locust Locusta migratoria from low-altitude and high-altitude regions were compared under 2 oxygen levels:normoxia(i.e.,21 kPa oxygen partial pressure and mild hypoxia(i.e.,10 kPa oxygen partial pressure).Our results demonstrated that,whether reared under normoxia or mild hypoxia,L.migratoria from high-altitude populations had longer developmental times,reduced weight,and lower mean relative growth rate as compared with those from low-altitude populations.When transferred from normoxia to mild hypoxia,nearly all the tested lifehistory traits presented significant negative changes in the low-altitude populations,but not in the high-altitude populations.The factor'strain'alone explained 18.26%-54.59%of the total variation for traits,suggesting that the phenotypic differences between L.migratoria populations from the 2 altitudes could be driven by genetic variation.Significant genetic correlations were found between life-history traits,and most of these showed differentiation between the 2 altitudinal gradients.G-matrix comparisons showed significant structural differences between L.migratoria from the 2 regions,as well as several negative covariances(i.e.,trade-offs)between traits in the low-altitude populations.Overall,our study provides clear evidence that evolutionary divergence of embryonic traits between L.migratoria populations from different altitudes has occurred.

Testing for selection on color and pattern in a mimetic radiation

In this paper, we analyze variation in spectral reflectance and color pattern among populations to demonstrate dra-matic divergence between four distinct morphs of the mimic poison frog Ranitomeya imitator. We also analyze genetic diver-gence in d-loop mtDNA sequences between populations. We then use coalescent-based simulations to demonstrate that the high levels of observed phenotypic divergence are not consistent with levels of genetic divergence expected under neutral drift among populations, implying an important role for selection in driving divergence between these populations .