Sex-Specific Arrival Times on the Breeding Grounds: Hybridizing Migratory Skuas Provide Empirical Support for the Role of Sex Ratios.

In migratory animals, protandry (earlier arrival of males on the breeding grounds) prevails over protogyny (females preceding males). In theory, sex differences in timing of arrival should be driven by the operational sex ratio, shifting toward protogyny in female-biased populations. However, empirical support for this hypothesis is, to date, lacking. To test this hypothesis, we analyzed arrival data from three populations of the long-distance migratory south polar skua (Catharacta maccormicki). These populations differed in their operational sex ratio caused by the unidirectional hybridization of male south polar skuas with female brown skuas (Catharacta antarctica lonnbergi). We found that arrival times were protandrous in allopatry, shifting toward protogyny in female-biased populations when breeding in sympatry. This unique observation is consistent with theoretical predictions that sex-specific arrival times should be influenced by sex ratio and that protogyny should be observed in populations with female-biased operational sex ratio.

Introgressive hybridization and the evolutionary history of the herring gull complex revealed by mitochondrial and nuclear DNA.

BACKGROUND: Based on extensive mitochondrial DNA (mtDNA) sequence data, we previously showed that the model of speciation among species of herring gull (Larus argentatus) complex was not that of a ring species, but most likely due more complex speciation scenario's. We also found that two species, herring gull and glaucous gull (L. hyperboreus) displayed an unexpected biphyletic distribution of their mtDNA haplotypes. It was evident that mtDNA sequence data alone were far from sufficient to obtain a more accurate and detailed insight into the demographic processes that underlie speciation of this complex, and that extensive autosomal genetic analysis was warranted. RESULTS: For this reason, the present study focuses on the reconstruction of the phylogeographic history of a limited number of gull species by means of a combined approach of mtDNA sequence data and 230 autosomal amplified fragment length polymorphism (AFLP) loci. At the species level, the mtDNA and AFLP genetic data were largely congruent. Not only for argentatus and hyperboreus, but also among a third species, great black-backed gull (L. marinus) we observed two distinct groups of mtDNA sequence haplotypes. Based on the AFLP data we were also able to detect distinct genetic subgroups among the various argentatus, hyperboreus, and marinus populations, supporting our initial hypothesis that complex demographic scenario's underlie speciation in the herring gull complex. CONCLUSIONS: We present evidence that for each of these three biphyletic gull species, extensive mtDNA introgression could have taken place among the various geographically distinct subpopulations, or even among current species. Moreover, based on a large number of autosomal AFLP loci, we found evidence for distinct and complex demographic scenario's for each of the three species we studied. A more refined insight into the exact phylogeographic history within the herring gull complex is still impossible, and requires detailed autosomal sequence information, a topic of our future studies.

On the origin of MADS-domain transcription factors.

MADS-domain transcription factors are involved in signal transduction and developmental control in plants, animals and fungi. Because their diversification is linked to the origin of novelties in multicellular eukaryotes, the early evolution of MADS-domain proteins is of interest, but has remained enigmatic. Employing whole genome sequence information and remote homology detection methods, we demonstrate that the MADS domain originated from a region of topoisomerases IIA subunit A. Furthermore, we provide evidence that gene duplication occurred in the lineage that led to the MRCA of extant eukaryotes, giving rise to SRF-like and MEF2-like MADS-box genes.

Floral visitation and reproductive traits of Stamenoid petals, a naturally occurring floral homeotic variant of Capsella bursa-pastoris (Brassicaceae).

Homeotic changes played a considerable role during the evolution of flowers, but how floral homeotic mutants initially survive in nature has remained enigmatic. To better understand the evolutionary potential of floral homeotic mutants, we established as a model system Stamenoid petals (Spe), a natural variant of Capsella bursa-pastoris (Brassicaceae). In the flowers of Spe plants, petals are transformed into stamens, whereas all other floral organs are unaffected. In contrast with most other homeotic mutants, the Spe variant occurs in relatively stable populations in the wild. In order to determine how the profound change in floral architecture influences plant performance in the wild, we performed common garden experiments running over 3 years. Here, we show that Spe and wild-type plants attract the same assemblage of floral visitors: mainly hoverflies, wild bees and thrips. However, floral visitation is about twice as frequent in wild-type plants as in Spe plants. Nevertheless, the numbers of seeds per fruit were about the same in both variants. Wild-type plants produced more flowers, fruits and seeds per plant than Spe plants, whereas the germination capacity of Spe seeds was higher than that of the wild-type. Determination of volatile composition revealed monoterpenes and 3,4-dimethylbenzaldehyde, which were detected only in wild-type flowers, presumably because they are produced only by petals. Our data indicate that the similar fitness of Spe and wild-type C. bursa-pastoris in the field results from complex compensation between plant architecture and germination capacity. In contrast, flower structure and floral visitation are only of minor importance, possibly because C. bursa-pastoris is mainly self-pollinating.

Phylogeography of the southern skua complex-rapid colonization of the southern hemisphere during a glacial period and reticulate evolution.

Whilst we have now a good understanding how past glaciation influenced species at the northern hemisphere, our knowledge of patterns and modes of speciation is far more limited for the southern hemisphere. We provide mtDNA based data on the phylogeography of a circumpolar distributed southern hemisphere seabird group-the southern skua complex (Catharacta spp.). Diversification of southern skuas dates between 210,000 yBP and 150,000 yBP and coincides with a glacial spanning 230,000-140,000 yBP. Skuas most likely first inhabited the Antarctic continent, in the course of global cooling and increasing glaciation spread to the sub-antarctic islands and Tristan da Cunha and finally colonized Patagonia and the Falkland Islands at the glacial maximum. Despite significant differences between taxa most populations still exchange genes with neighboring populations of other taxa and speciation is incomplete.