Endorsing Darwin – Global biogeography of the epipelagic goose barnacles Lepas spp. (Cirripedia, Lepadomorpha) proves cryptic speciation

Abstract

AimWe studied different species of gooseneck barnacles from the globally distributed rafting genus Lepas to examine whether the most widespread species are true cosmopolitans and to explore the factors influencing the phylogeny and biogeography of these epipelagic rafters.Location Temperate and tropical parts of the Atlantic, Pacific, and Indic oceans. MethodsWe used a phylogenetic approach based on mitochondrial 16S and coI sequences, and the nuclear 18S gene to elucidate patterns of inter-and intra-species divergence. Altogether, five species of Lepas from 18 confined regions of the Atlantic, Pacific and Indic oceans were analyzed.Results A combination of nuclear and mitochondrial sequences provided robust phylogenetic signals for biogeographic classification of subgroups in Lepas species. Lepas australis, restricted to cold-temperate waters of the southern hemisphere shows two separate populations in the southern hemisphere (coastal Chile, other circum-Antarctic sampling sites) most probably related to temperature differences in the southern Pacific current systems. A more complex differentiation is seen for the cosmopolitan L. anatifera that thrives in warmer waters. In total, it is differentiated in four regional subgroups (coastal Chile, Oregon, Indopacific in general, Atlantic) and a global group, which might be either an ancient stemgroup, but more probably is an anthropogenic artefact. Separation into subgroups likely reflect geological vicariance effects. For Lepas, these were closure of the Isthmus of Panama, installation of the cool Benguela Current in the later Miocene including its persistence into the Present, Pleistocene current systems in the western Pacific differing from today, and in general lowered Pleistocene temperatures, and finally present-day current systems. The extreme ecological p r e p r i n t generalists L. anserifera and L. pectinata are not differentated according to available data and might represent true global species. Data for L. testudinata remain ambiguous. Main conclusionsOur data indicate cryptic speciation in some but not all species of the cosmopolitan epipelagic genus Lepas. Regional distribution of genetically different populations rely on a wealth of in part interacting inherited geological factors and modern traits. Controlling factors differ between species according to their ecospace limits and demonstrate the need for studies on species level to avoid unjustified generalizations. Data indicate that allopatric speciation is the main mode of divergence. True global species, if existent at all, need to be extreme ecological generalists, like Lepas pectinata and L. anserifera.

Genomic insights into the sessile life and biofouling of barnacles (Crustacea: Cirripedia)

“…For coastal marine species (including barnacles), the rapid cooling and expansion of glaciers caused a drastic reduction in the sea level and led to a decrease in available coastal habitat, resulting in fragmented populations, genetic bottleneck and population restructuring ( Ludt and Rocha, 2015 ; Tsang et al, 2012 ). In addition, since adult L. anserifera usually attaches to floating objects and are transported by ocean currents which may enhance their genetic connectivity ( Buckeridge, 2012 ; Schiffer and Herbig, 2016 ), the genetic variation and population size of L. anserifera was estimated to be larger than those of the A. amphitrite , which usually inhabits rocky shores.

Figure 2 Demographic history inferred from barnacle genomes.

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The mitochondrial genomes of the acoelomorph worms Paratomella rubra, Isodiametra pulchra and Archaphanostoma ylvae

“…This, and the differences on the nucleotide level, including the relatively low level of similarity in the cox1 barcoding gene might indicate that P. rubra collected from Barcelona (Spain) 26 and our animals from Yorkshire (England) should be regarded as cryptic species and not just divergent populations. Given the large and mostly unresolved diversity in benthic communities 39 , and the marine environment in general 40 , a differentiation into (cryptic) species cannot be seen as surprising.…”

The ecology of Lepas-based biofouling communities on moored and drifting objects, with applications for marine forensic science

“…We propose that L. anserifera be considered as a valuable indicator species in marine forensic science, based on its patterns of community succession, its usefulness in isotopic analyses, its high abundance, cosmopolitan distribution (Schiffer and Herbig 2016) and comparative ease of field identification, providing a useful regional-level tool for determining the water temperatures in which they formed, and allowing the origin and path of drifting debris to be estimated.…”