Testing for reproductive isolation among sympatrically diverging lineages is a key prerequisite for understanding speciation processes. Recent genome‐wide studies of the wing‐dimorphic New Zealand stonefly Zelandoperla fenestrata have revealed evidence for ecological speciation among sympatric ecotype pairs, but the basis for their apparent reproductive isolation remains unclear. We conduct paired mating tests among co‐distributed Z. fenestrata ecotypes from southern South Island to test for prezygotic barriers contributing to their reproductive isolation and divergence. Experimental data reveal assortative mating among ecotypes, with strong differentiation in the duration of matings between matched‐ecotype pairs relative to non‐matched pairs. These findings add weight to the hypothesis that assortative mating can be a key mechanism facilitating rapid ecological speciation of sympatric ecotypes. Our study also represents the first documentation of mating behaviours in the Southern Hemisphere stonefly suborder Antarctoperlaria.
Range-restricted upland taxa are prone to population bottlenecks and thus typically have low genetic diversity, making them particularly vulnerable to environmental change. In this study, we used a combination of genotyping-by-sequencing (10,419 SNPs) and mitochondrial COI sequencing to test for population genetic structure within the narrow-range flightless sub-alpine stonefly Zelandoperla maungatuaensis Foster. This species is restricted to only a handful of upland streams along a 4 km stretch of the isolated Maungatua range in southeast New Zealand. We identified striking genetic structure across the narrow range of Z. maungatuaensis, with three deeply divergent allopatric lineages detected. These distinct lineages likely diverged in the early-mid Pleistocene, apparently persisting in separate microrefugia throughout subsequent glacial cycles. Our results illustrate how secondary flight loss can facilitate insect diversification across fine spatial scales, and demonstrate that intraspecific phylogenetic diversity cannot necessarily be predicted from range-size alone. Additional demographic analyses are required to better understand the conservation status of these divergent Z. maungatuaensis lineages, and to assess their potential susceptibility to climate change and other anthropogenic impacts.
The evolution of Batesian mimicry – whereby harmless species avoid predation through their resemblance to harmful species – has long intrigued biologists. In rare cases, such mimicry systems can be highly dynamic, being maintained via frequency-dependent selection on intraspecific polymorphisms, in which only some individuals within a population resemble a noxious ‘model’. Here, we use genomic approaches to identify the genetic basis of a striking mimicry polymorphism within a widespread New Zealand stonefly complex. Specifically, highly melanised specimens of Zelandoperla closely resemble an aposematic stonefly (Austroperla cyrene) well-known for its production of hydrogen cyanide. We assess convergence in the colour pattern of these two species, compare their relative palatability to predators, and use genome-wide association mapping to elucidate the genetic basis of this mimicry polymorphism. Our analysis reveals that melanised Zelandoperla overlap significantly with Austroperla in colour space, but are significantly more palatable to predators, indicating that they are indeed Batesian mimics. Analysis of 194,773 genome-wide SNPs reveals a strong outlier locus (ebony) differentiating melanic (mimic) versus non-melanic phenotypes. As ebony has a well-documented role in insect melanin biosynthesis, our findings highlight its conserved function across deeply divergent hexapod lineages. Distributional records suggest a link between the occurrence of Zelandoperla mimics and forested ecosystems where the model Austroperla is abundant, suggesting the potential for adaptive shifts in this system underpinned by environmental change.
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