Spatial Variation of Acanthophlebia cruentata (Ephemeroptera), a Mayfly Endemic to Te Ika-a-Māui—North Island of Aotearoa, New Zealand

Simple Summary

Patterns of variation within a widespread species can provide evidence of population history. Adjacent stable populations with gene flow show clinal genetic divergence forming a pattern of isolation by distance. Populations that have grown due to an increase in potential habitat such as forest cover since the last glacial maximum will have low genetic variation showing patterns of range expansion. The mayfly Acanthophlebia cruentata of Aotearoa, New Zealand, is widespread in streams of North Island but absent from the cooler South Island. Mayfly nymphs are restricted to streams but adults fly, facilitating gene flow among catchments. We detected higher genetic diversity at lower latitudes of this mayfly’s range compared to most of its distribution, concordant with predictions of limited forest cover in New Zealand during Pleistocene glacial periods. A signature of recent range expansion was observed in the higher latitudes. Despite initial observation suggesting mayfly size correlated with latitude, we found sex, elevation and sampling date were significant predictors of size, and some size variation is also explained by three regional groups based on haplotype distribution.

Abstract

The mayfly Acanthophlebia cruentata of Aotearoa, New Zealand, is widespread in Te Ika-a-Māui North Island streams, but has never been collected from South Island despite land connection during the last glacial maximum. Population structure of this mayfly might reflect re-colonisation after volcanic eruptions in North Island c1800 years ago, climate cycling or conceal older, cryptic diversity. We collected population samples from 33 locations to estimate levels of population genetic diversity and to document phenotypic variation. Relatively low intraspecific haplotype divergence was recorded among mitochondrial cytb sequences from 492 individuals, but these resolved three geographic-haplotype regions (north, west, east). We detected a signature of isolation by distance at low latitudes (north) but evidence of recent population growth in the west and east. We did not detect an effect of volcanic eruptions but infer range expansion into higher latitudes from a common ancestor during the last glacial period. As judged from wing length, both sexes of adult mayflies were larger at higher elevation and we found that haplotype region was also a significant predictor of Acanthophlebia cruentata size. This suggests that our mitochondrial marker is concordant with nuclear genetic differences that might be explained by founder effect during range expansion.

Phylogeography reveals the complex impact of the Last Glacial Maximum on New Zealand's terrestrial biota

We review the major phylogeographic patterns in Aotearoa New Zealand's terrestrial flora and fauna that have been associated with the Ōtira Glaciation of the Pleistocene, the end of which coincides with the global Last Glacial Maximum (LGM). We focus on (1) the complexity of biogeographic histories of New Zealand species, with LGM-driven phenomena overlaying the impacts of mountain-building and other drivers of phylogeographic structure; (2) the locations of glacial refugia and sets of taxa which may have shared refugia; and (3) the role of glaciation in driving diversification. We end with a brief focus on the next directions, including what can we learn about New Zealand's glacial history by expanding our phylogeographic toolbox to include genomic methods and hypothesis-driven inference methods. We provide follow-up questions which take advantage of the wealth of phylogeographic data for New Zealand.

Insights into Aotearoa New Zealand's biogeographic history provided by the study of natural hybrid zones

Hybridisation is commonly observed in geographical zones of contact between distinct lineages. These contact zones have long been of interest for biogeographers because they provide insight into the evolutionary and ecological processes that influence the distribution of species as well as the process of speciation. Here we review research on hybrid zones and zones of past introgression, both terrestrial and marine, in Aotearoa New Zealand. Many of New Zealand's hybrid zones occur between lineages or species that diverged prior to the Last Glacial Maximum (LGM), with numerous divergences dating to the early Pleistocene or Pliocene. Few secondary contact zones have been detected in terrestrial plants and in marine taxa. This may reflect a lack of the intensive sampling required to detect hybrid zones in these groups but for plants may also indicate widespread Pleistocene survival across the country. Lastly, we suggest avenues for research into New Zealand hybrid zones that are likely to be fruitful.

Phylogeography of the Cran’s bully Gobiomorphus basalis (Gobiiformes: Eleotridae) and an analysis of species boundaries within the New Zealand radiation of Gobiomorphus

New Zealand has a complex recent history of climatic and tectonic change that has left variable signatures in the geographic distribution and genetic structure of the region’s flora and fauna. To identify concordant patterns, a broad range of taxa must be examined and compared. In New Zealand’s North Island, a consensus is forming as to the dominant biogeographic barriers in the region although obligate freshwater taxa have not been considered in this framework. We use single-nucleotide polymorphisms to investigate phylogeography in the widespread obligate freshwater fish Gobiomorphus basalis on the North Island. Phylogeographic patterns within G. basalis reveal biogeographic disjunctions that are in some ways consistent and in other ways at odds with established patterns, providing insight into the processes that have shaped the islands’ biogeography. We also use phylogeography to delineate species boundaries within the entire New Zealand radiation of Gobiomorphus and find that it contains several morphologically cryptic species. We resolve two clades within G. basalis that correspond to areas north and south of the Taupo Volcanic Zone. We confirm the distinctiveness of Gobiomorphus alpinus relative to Gobiomorphus cotidianus, as well as the presence of two lineages within Gobiomorphus breviceps that were previously identified based on mitochondrial data.