Understanding evolutionary processes during past Quaternary climatic cycles: Can it be applied to the future?

Climate change affected ecological community make-up during the Quaternary which was probably both the cause of, and was caused by, evolutionary processes such as species evolution, adaptation and extinction of species and populations

Limited genomic divergence between intraspecific forms of Culex pipiens under different ecological pressures

Abstract Background: Divergent selection can be a major driver of ecological speciation. In insects of medical importance, understanding the speciation process is both of academic interest and public health importance. In the West Nile virus vector Culex pipiens, intraspecific pipiens and molestus forms vary in ecological and physiological traits. Populations of each form appear to share recent common ancestry but patterns of genetic differentiation across the genome remain unknown. Here, we undertook an AFLP genome scan on samples collected from both sympatric and allopatric populations from Europe and the USA to quantify the extent of genomic differentiation between the two forms. Results: The forms were clearly differentiated but each exhibited major population sub-structuring between continents. Divergence between pipiens and molestus forms from USA was higher than in both inter- and intra-continental comparisons with European samples. The proportion of outlier loci between pipiens and molestus (≈3 %) was low but consistent in both continents, and similar to those observed between sibling species of other mosquito species which exhibit contemporary gene flow. Only two of the outlier loci were shared between inter-form comparisons made within Europe and USA. Conclusion: This study supports the molestus and pipiens status as distinct evolutionary entities with low genomic divergence. The low number of shared divergent loci between continents suggests a relatively limited number of genomic regions determining key typological traits likely to be driving incipient speciation and/or adaptation of molestus to anthropogenic habitats

Neural divergence and hybrid disruption between ecologically isolated Heliconius butterflies

The importance of behavioral evolution during speciation is well established, but we know little about how this is manifest in sensory and neural systems. A handful of studies have linked specific neural changes to divergence in host or mate preferences associated with speciation. However, the degree to which brains are adapted to local environmental conditions, and whether this contributes to reproductive isolation between close relatives that have diverged in ecology, remains unknown. Here, we examine divergence in brain morphology and neural gene expression between closely related, but ecologically distinct, Heliconius butterflies. Despite ongoing gene flow, sympatric species pairs within the melpomene–cydno complex are consistently separated across a gradient of open to closed forest and decreasing light intensity. By generating quantitative neuroanatomical data for 107 butterflies, we show that Heliconius melpomene and Heliconius cydno clades have substantial shifts in brain morphology across their geographic range, with divergent structures clustered in the visual system. These neuroanatomical differences are mirrored by extensive divergence in neural gene expression. Differences in both neural morphology and gene expression are heritable, exceed expected rates of neutral divergence, and result in intermediate traits in first-generation hybrid offspring. Strong evidence of divergent selection implies local adaptation to distinct selective optima in each parental microhabitat, suggesting the intermediate traits of hybrids are poorly matched to either condition. Neural traits may therefore contribute to coincident barriers to gene flow, thereby helping to facilitate speciation

Mutualisms within light microhabitats are associated with sensory convergence in a mimetic butterfly community

Niche partitioning within variable habitats can expose species to distinct sensory information. Vision is the primary sensory modality used by many animals to interact with their habitat. However, the role of terrestrial light environment properties in shaping species assemblages and visual system evolution is not fully understood. By studying a diverse, sympatric community of mimetic butterflies, we demonstrate that forest architecture creates a mosaic of light microhabitats that drive adaptive sensory convergence and divergence in both peripheral and central sensory systems. Our results show that across the visual system, predictable patterns of evolution characterize how species adapt to the availability of sensory information within their preferred light microhabitat. Our study provides an example of how visual systems consistently respond to their external sensory world, and illustrates the wide-reaching consequences of interspecific mutualisms, such as Müllerian mimicry, on organismal evolution.</jats:p

Patterns of visual adaptation in tropical mimetic butterflies

Species diversity within an ecosystem can be supported by favouring microhabitat specialisation. In complex habitats, like tropical rainforests, spatial and temporal segregation across microhabitats can expose species to distinct sensory realms. For many animals, visual systems serve as the primary conduit for perceiving biologically relevant sensory information, and the structural and functional variety of eyes and sensory brain regions reflects their critical role in diverse animal behaviours. However, little is known of their role in mediating niche segregation across subtle ecological scales, particularly in terrestrial environments. I explore the role of microhabitat partitioning in driving predictable patterns of adaptive visual system evolution within two diverse radiations of mimetic Neotropical butterfly, the Heliconius and Ithomiini. By taking a comparative approach, I investigate whether dual patterns of habitat divergence and convergence is manifested in the visual system at the perceptual, processing, and molecular level. I find extensive evidence of heritable, habitat-associated visual system variation, particularly for neural processing structures, hinting at the evolutionary lability of these systems to rapidly accommodate local adaptations to visual ecologies. My research also empirically demonstrates, for the first time, how variation in forest structure can give rise to distinct photic environments, highlighting the role of spectral variation as a major driver of adaptive community assemblage within a terrestrial forest radiation. In addition, evidence of visual morphological convergence offers a mechanistic insight into the evolvability of visual adaptations when confronted with similar ecological challenges, shedding light on their significance in promoting ecological diversification and speciation

The sensory ecology of speciation

In this chapter, we explore the potential influence of sensory ecology on speciation, including but not limited to the concept of sensory drive, which concerns the co-evolution of signals and sensory systems with the local environment. The sensory environment can influence individual fitness in a variety of ways, thereby affecting the evolution of both pre- and post-mating reproductive isolation. Previous work focused on sensory drive has undoubtedly advanced the field, but we argue that it may have also narrowed our understanding of the broader influence of the sensory ecology on speciation. Moreover, the clearest examples of sensory drive are largely limited to aquatic organisms, which may skew the influence of contributing factors. We review the evidence for sensory drive across environmental conditions, and in this context discuss the importance of more generalized effects of sensory ecology on adaptive behavioral divergence. Finally, we consider the potential of rapid environmental change to influence reproductive barriers related to sensory ecologies. Our synthesis illustrates the importance of sensory conditions for local adaptation and divergence in a range of behavioral contexts and extends our understanding of the interplay between sensory ecology and speciation