Have we so far only seen the tip of the iceberg? Exploring species diversity and distribution of the giant amphipod Eurythenes

Abstract

Additional material of the iconic giant amphipod Eurythenes was investigated. Recently, the species E. gryllus has been separated into 12 distinct species-level lineages of which several have been described as distinct species, based on both morphology and genetics. This study revealed three additional species-level lineages from unique sampling localities, showing that with minimal sampling effort, species diversity within Eurythenes can still increase. One species-level lineage was found in the Indian Ocean and another one in the Pacific, which was subsequently identified as E. thurstoni. In addition to the three species already reported from the Southern Ocean (E. maldoror, E. gryllus s.s. and E. andhakarae), a supplementary bathyal species was found in the Weddell Sea. E. gryllus was confirmed to be amphitropical including newly sampled localities around the Kerguelen Islands and additional samples from the Svalbard Archipelago. Building on new and earlier data, geographic and bathymetric distributions of the different species that have been discovered so far are presented here and several factors are evaluated for their likelihood of having triggered past speciation events in this scavenger. Topographic and hydrographical features are discussed but rejected as sufficient reasons for the distributional patterns observed. Bathymetric segregation is interpreted with regard to what is known about the ecology of the species. The previously reported genetic break around 3000 m persists in this new data-set for all species but one. This study underlines the need of processing all individuals sampled, since two or more sympatric species are found in different proportions, and that conclusions regarding diversity and distribution may drastically change when increasing sampling intensity and coverage. Finally, I suggest here that only a mere fraction of all Eurythenes species has yet been discovered and that a more complete knowledge of the ecology of the species is of paramount importance for interpreting their evolution.

Macaronesian islands as promoters of diversification in amphipods: The remarkable case of the family Hyalidae (Crustacea, Amphipoda)

“…Sympatric speciation could be one possible explanation for these co‐occurrences of multiple MOTUs. This type of evolutionary process is controversial, has not been completely understood yet and could be mistaken for microallopatry (Fitzpatrick, Fordyce, & Gavrilets, ) when this is related to a shift in ecological preference of the divergent species, as for the plant host for phytophagous insects (Berlocher & Feder, ), the possible feeding strategies of amphipods belonging to the genus Eurythenes (Havermans, ) or the host of the arctic amphipod Parampithoe hystrix Ross 1835 (Schnabel & Hebert, ). Nonetheless, the possibility of a shift in the ecological habits of A. stebbingi , such as the preference for different algae as food or during their life cycle, is a possibility but, further studies are needed to confirm this hypothesis.…”

Cryptic species as a window into the paradigm shift of the species concept

“…The number of cryptic species within nominal species varies up to several tens of species (Havermans, 2016;Katouzian et al, 2016;Mamos et al, 2016;Witt et al, 2006). Ecological diversity of amphipods allows for testing generalities in processes generating cryptic diversity under different ecological settings.…”

Taxonomy and phylogeny of mud owls (Annelida: Sternaspidae), including a new synonymy and new records from the Southern Ocean, North East Atlantic Ocean and Pacific Ocean: challenges in morphological delimitation

“…Low genetic diversity over great horizontal distances has been reported for a number of deep-sea invertebrate taxa (e.g. Etter et al 2011;Georgieva et al 2015;Zhang et al 2015;Havermans 2016;Kobayashi et al 2018;Kobayashi and Araya 2018). Cold environments are known to slow larval metabolism (Shilling and Manahan 1994) and Kobayashi et al (2018) suggest that the colder temperatures of deep-sea waters may arrest larval sternaspid metabolism and development, which, in addition to deep-water countercurrents that circulate along central Japan to the Aleutian Peninsula (Kawabe and Fujio 2010), allows for greater dispersion S. cf.…”