Multiple Doris “kerguelenensis” (Nudibranchia) species span the Antarctic Polar Front

Abstract

Despite strong historical biogeographical links between benthic faunal assemblages of the Magellan region of South America and the Antarctic Peninsula, very few studies have documented contemporary movement and gene flow in or out of the Southern Ocean, especially across the Antarctic Polar Front (APF). In fact, oceanographic barriers such as the APF and Antarctica's long geologic isolation have substantially separated the continents and facilitated the evolution of endemic marine taxa found within the Antarctic region. The Southern Ocean benthic sea slug complex, Doris “kerguelenensis,” are a group of direct‐developing, simultaneous hermaphrodites that lack a dispersive larval stage. To date, there are 59 highly divergent species known within this complex. Here, we provide evidence to show intraspecific genetic connectivity occurs across the APF for multiple species within the D. “kerguelenensis” nudibranch species complex. We addressed questions of genetic connectivity by examining the phylogeographic structure of the three best‐sampled D. “kerguelenensis” species and another three trans‐APF species using the protein coding mtDNA gene, cytochrome oxidase I. We also highlight alternative refugia uses among species with the same life history traits (i.e., benthic and direct developers) and for some species, extremely large distributions are established (e.g., circumpolarity). By improving our sampling of these nudibranchs, we gain better insight into the population structure and connectivity of the Antarctic region. This work also demonstrates how difficult it is to make generalizations across Antarctic marine species, even among ecologically‐similar, closely related species.

The Phyloperiodic Approach Removes the “Cryptic Species” and Puts forward Multilevel Organismal Diversity

“…Thus, the periodic framework is not just a theoretical addition to existing practical methods, but also a key element for truly integrative study. Currently, in applying the controversial concept of "cryptic species", a substantial part of the diversity remains unnamed [66], whereas the phyloperiodic approach and multilevel organismal diversity (MOD) method allow us to name each particular small unit of diversity. This is a very important practical achievement (including conservation biology) that immediately distinguishes the phyloperiodic and MOD approaches from the notion of "integrative taxonomy" since the latter does not necessarily recognize morphodiversity and does not necessarily allow all molecularly distinct groups to be named [34,44].…”