A pinboard by
Christine Ewers

Postdoc, Christian-Albrechts University


Androdioecy was first described by Darwin in his seminal work on barnacle diversity; he was the first to identify dwarfed males and large hermaphrodites in the same reproductive populations. Despite Darwin's evidence for androdioecy, it was declared absent from nature in the 1980s, only to later be rediscovered in phylogenetically diverse taxa. We assessed the evolutionary dynamics of the androdioecious barnacle <i>Chelonibia testudinaria</i> (Linneaus, 1758). Combining field assays, laboratory trials and genetic parentage assignment studies, we characterized its mating system, sex allocation and life history. We compared those findings to theoretical expectations and other, non-androdioecious systems, and show that males do not have a relative mating advantage, as expected by mating system theory, but that life history is sufficient to maintain androdioecy. Specifically, high mortality rates and early maturation of males maintains androdioecy in this system.


The oceanic concordance of phylogeography and biogeography: a case study in Notochthamalus

Abstract: Dispersal and adaptation are the two primary mechanisms that set the range distributions for a population or species. As such, understanding how these mechanisms interact in marine organisms in particular – with capacity for long‐range dispersal and a poor understanding of what selective environments species are responding to – can provide useful insights for the exploration of biogeographic patterns. Previously, the barnacle Notochthamalus scabrosus has revealed two evolutionarily distinct lineages with a joint distribution that suggests an association with one of the two major biogeographic boundaries (~30°S) along the coast of Chile. However, spatial and genomic sampling of this system has been limited until now. We hypothesized that given the strong oceanographic and environmental shifts associated with the other major biogeographic boundary (~42°S) for Chilean coastal invertebrates, the southern mitochondrial lineage would dominate or go to fixation in locations further to the south. We also evaluated nuclear polymorphism data from 130 single nucleotide polymorphisms to evaluate the concordance of the signal from the nuclear genome with that of the mitochondrial sample. Through the application of standard population genetic approaches along with a Lagrangian ocean connectivity model, we describe the codistribution of these lineages through a simultaneous evaluation of coastal lineage frequencies, an approximation of larval behavior, and current‐driven dispersal. Our results show that this pattern could not persist without the two lineages having distinct environmental optima. We suggest that a more thorough integration of larval dynamics, explicit dispersal models, and near‐shore environmental analysis can explain much of the coastal biogeography of Chile.

Pub.: 07 Jun '16, Pinned: 20 Jun '17

The unexpected mating system of the androdioecious barnacle Chelonibia testudinaria (Linnaeus 1758)

Abstract: Androdioecy was first described by Darwin in his seminal work on barnacle diversity; he identified males and hermaphrodites in the same reproductive population. Today, we realize that many androdioecious plants and animals share astonishing similarities, particularly with regard to their evolutionary history and mating system. Notably, these species were ancestrally dioecious, and their mating system has the following characteristics: hermaphrodites self‐fertilize frequently, males are more successful in large mating groups, and males have a mating advantage. A male mating advantage makes androdioecy more likely to persist over evolutionary times. Androdioecious barnacles, however, appear to persist as an outlier with a different evolutionary trajectory: they originate from hermaphroditic species. Although sexual systems of androdioecious barnacles are known, no information on the mating system of androdioecious barnacles is available. This study assessed the mating system of the androdioecious barnacle Chelonibia testudinaria. In contrast to other androdioecious species, C. testudinaria does not self‐fertilize, males do not have a mating advantage over hermaphrodites, and the average mating group is quite small, averaging only three individuals. Mating success is increased by proximity to the mate and penis length. Taken together, the mating system of C. testudinaria is unusual in comparison with other androdioecious plants and animals, and the lack of a male mating advantage suggests that the mating system alone does not provide an explanation for the maintenance of androdioecy in this species. Instead, we propose that sex‐specific life history equalizes male and hermaphroditic overall fitness.

Pub.: 28 Mar '16, Pinned: 20 Jun '17