Sex determination in the androdioecious barnacleScalpellum scalpellum(Crustacea: Cirripedia)

The evolutionary diversity of barnacles, with an updated classification of fossil and living forms

We present a comprehensive revision and synthesis of the higher-level classification of the barnacles (Crustacea: Thecostraca) to the genus level and including both extant and fossils forms. We provide estimates of the number of species in each group. Our classification scheme has been updated based on insights from recent phylogenetic studies and attempts to adjust the higher-level classifications to represent evolutionary lineages better, while documenting the evolutionary diversity of the barnacles. Except where specifically noted, recognized taxa down to family are argued to be monophyletic from molecular analysis and/or morphological data. Our resulting classification divides the Thecostraca into the subclasses Facetotecta, Ascothoracida and Cirripedia. The whole class now contains 14 orders, 65 families and 367 genera. We estimate that barnacles consist of 2116 species. The taxonomy is accompanied by a discussion of major morphological events in barnacle evolution and justifications for the various rearrangements we propose.

Sponge symbiosis is facilitated by adaptive evolution of larval sensory and attachment structures in barnacles

Symbiotic relations and range of host usage are prominent in coral reefs and crucial to the stability of such systems. In order to explain how symbiotic relations are established and evolve, we used sponge-associated barnacles to ask three questions. (1) Does larval settlement on sponge hosts require novel adaptations facilitating symbiosis? (2) How do larvae settle and start life on their hosts? (3) How has this remarkable symbiotic lifestyle involving many barnacle species evolved? We found that the larvae (cyprids) of sponge-associated barnacles show a remarkably high level of interspecific variation compared with other barnacles. We document that variation in larval attachment devices are specifically related to properties of the surface on which they attach and metamorphose. Mapping of the larval and sponge surface features onto a molecular-based phylogeny showed that sponge symbiosis evolved separately at least three times within barnacles, with the same adaptive features being found in all larvae irrespective of phylogenetic relatedness. Furthermore, the metamorphosis of two species proceeded very differently, with one species remaining superficially on the host and developing a set of white calcareous structures, the other embedding itself into the live host tissue almost immediately after settlement. We argue that such a high degree of evolutionary flexibility of barnacle larvae played an important role in the successful evolution of complex symbiotic relationships in both coral reefs and other marine systems.

Microsatellite DNA markers applicable to paternity inference in the androdioecious gooseneck barnacle Octolasmis warwickii (Lepadiformes: Poecilasmatidae)

The gooseneck barnacle Octolasmis warwickii has a rare sexual system called androdioecy, in which hermaphrodites and dwarf males co-occur. It has been hypothesized that dwarf males can coexist with conspecific hermaphrodites when dwarf males are capable of leaving more offspring than hermaphrodites via male reproduction. This hypothesis of reproductive superiority of dwarf males can be validated by comparing the reproductive success between dwarf males and hermaphrodites through DNA marker-based parentage testing. In the present study, we developed microsatellite DNA markers for O. warwickii, and evaluated the power of these markers to infer parentage based on simulation analysis. Using next generation sequencing, we obtained 344 microsatellite sequences suitable for designing primer sets for amplification in polymerase chain reaction (PCR). Of these, we examined the PCR amplification efficiency of 54 primer sets, of which 11 passed our primer screening in a population sample (n = 35). The developed markers exhibited moderate to high levels of polymorphisms, and met Hardy-Weinberg equilibrium with little evidence of significant allelic association to each other. Our simulated paternity inference suggested that the combinational use of the markers allows a high resolution of parentage (success rate of > 99.9%) if all candidate fathers are available.