Incipient speciation and its impact on taxonomic decision: a case study using a sky island sister-species pair of stag beetles (Lucanidae: Lucanus)

Abstract

Species delimitation can be difficult when the divergence between focal taxa is in the incipient stage of speciation, because conflicting results are expected among different data sets, and the species limits can differ depending on the species concept applied. We studied speciation history and investigated the impact on taxonomic decision-making when using different types of data in a Taiwanese endemic sister-species pair of stag beetles, Lucanus miwai and Lucanus yulaoensis, from sky island habitats. We showed that the two geographical taxa can be diagnosed by male mandibular shape. We found two mitochondrial co1 lineages with pairwise sequence divergence > 3%; however, L. miwai might not be monophyletic. The result of our multispecies coalescent-based species delimitation using five nuclear loci supported the evolutionary independence of the two sister species, but the calculated values of the genealogical divergence index (gdi) corresponded to the ambiguous zone of species delimitation. We also showed that post-divergence gene flow is unlikely. Our study demonstrates challenges in the delineation of incipient species, but shows the importance of understanding the speciation history and adopting integrative approaches to reconcile seemingly conflicting results before making evolutionarily relevant taxonomic decisions.

Phylogenomics reveals within species diversification but incongruence with color phenotypes in widespread orchid bees (Hymenoptera: Apidae: Euglossini)

“…Alternatively, the geological history of the Choco suggests that the modern tropical rainforest landscape was only established by the early Pleistocene [∼2.7 Mya, Pérez-Escobar et al (2019)] and that individuals from the Amazon Forest might have dispersed to the Choco after the Andean uplift without exchanging much gene flow with the Central American lineage. We did not find evidence of morphological differentiation of this lineage compared to the other populations of E. meriana but it could certainly represent a case of incipient speciation (Mayr 1942, De Queiroz 2007) in which the Choco lineage is in the process of diverging but there is still ongoing gene flow (Chou et al 2021) and there are no clear color patterns or morphological characters that separate them (Ghisbain et al 2020). To confirm whether there is an ongoing speciation process, a detailed sampling should be conducted in this region in the area between Ecuador (Choco Region) and Costa Rica (Central America).…”

Genomic tools for comparative conservation genetics among three recently diverged stag beetles (Lucanus, Lucanidae)

“…Furthermore, statistically neglectable post-divergence gene flow among the three taxa indicated their independent evolutionary history since the divergences (Figure 4). The divergence among the three taxa of our study can be categorised as at the speciation initiation stage (Huang, 2020), facilitated by allopatric isolation possibly due to climate change and forest-habitat fragmentation in the Pleistocene (Chou et al, 2021).…”

“…Note that it is not unprecedented in insects that speciation initiated by an allopatric process could have been completed in fewer than 200 kya (Huang et al, 2020). In Asia, geographical taxa have frequently been reported to have originated around 100-600 kya (Chou et al, 2021;Dong et al, 2017;Morgan & Huang, 2021), where the geographic taxa may or may not be treated as different species (Chou et al, 2022;Dong et al, 2020).…”

“…We believe a Taiwanese endemic species complex of stag beetles, Lucanus miwai s.l. (Chou et al, 2021), which is composed of three closely related allopatric sky-island taxa may be a good empirical system to statistically and comparatively evaluate the genetic consequence of various anthropogenic exploitations.…”

“…L. miwai and its sister species Lucanus yulaoensis are stag beetles endemic to Taiwan (Chou et al, 2021; Figure 1). An additional closely related taxon geographically intermediate between the two sister species has recently been found in Miaoli County (Figure 1).…”