Markus S. Ritz

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.

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.

Vocal performance reflects individual quality in a nonpasserine

Recent studies on mate-quality recognition in passerines showed that females use subtle differences in sound production to assess males. We analysed long calls of brown skuas, Catharacta antarctica lonnbergi, to test whether vocal performance could serve as an indicator of individual quality in a nonpasserine species. Measurements of vocal performances focused on two acoustic parameters for which motor constraints have been reported in passerines, namely ‘vocal deviation’ and ‘peak performance’. As potential indicators of individual quality we measured body size, body condition (body mass corrected for size) and mean reproductive success. We found a triangular distribution of calls between note repetition rate and frequency bandwidth. Males performing long calls closer to the performance limit had a higher mean reproductive success than males that show long calls with a larger vocal deviation. Similarly, males calling with a high peak performance were more successful breeders than males with low peak performance. Our findings indicate that long calls of brown skuas are limited by motor constraints similar to vocalizations in passerines. We show that differences in vocal performance reflect males reproductive success with more successful breeders producing the more difficult calls. This implies that limits on vocal performance due to motor constraints present a suitable mechanism for mate-quality recognition in nonpasserine birds.

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

BackgroundBased 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 scenarios. 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.ResultsFor 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 scenarios underlie speciation in the herring gull complex.ConclusionsWe 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 scenarios 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.

Speciation and phylogeography of giant petrels Macronectes

We examine global phylogeography of the two forms of giant petrel Macronectes spp. Although previously considered to be a single taxon, and despite debate over the status of some populations and the existence of minimal genetic data (one mitochondrial cytochrome b sequence per form), the current consensus based on morphology is that there are two species, Northern Giant Petrel M. halli and Southern Giant Petrel M. giganteus. This study examined genetic variation at cytochrome b as well as six microsatellite loci in giant petrels from 22 islands, representing most island groups at which the two species breed. Both markers support separate species status, although sequence divergence in cytochrome b was only 0.42% (corrected). Divergence was estimated to have occurred approximately 0.2mya, but with some colonies apparently separated for longer (up to 0.5 my). Three clades were found within giant petrels, which separated approximately 0.7mya, with the Southern Giant Petrel paraphyletic to a monophyletic Northern Giant Petrel. There was evidence of past fragmentation during the Pleistocene, with subsequent secondary contact within Southern Giant Petrels. The analysis also suggested a period of past population expansion that corresponded roughly to the timing of speciation and the separation of an ancestral giant petrel population from the fulmar Fulmarus clade.

Factors affecting chick growth in the South Polar Skua (Catharacta maccormicki): food supply, weather and hatching date

This study investigated chick growth in a pelagic Antarctic seabird, the South Polar Skua (Catharacta maccormicki). The factors food supply, weather and hatching date were analysed in a population of 54 breeding pairs at King George Island/South Shetland Islands. Food supply was manipulated by offering fish corresponding to 20% of daily energy demand of chicks to half of the breeding pairs every second day. Growth of mass, head, wing and tarsus was followed and related to the treatment, weather conditions, hatching date and interactive effects. Food supply did not limit chick growth in the studied season. Parents seemed to try to feed their chicks at a maximum rate and succeeded in the studied season because the general food supply was very good. Low temperatures and strong winds depressed chick growth. A growth advantage of food-supplemented chicks could be observed when the natural conditions for chick growth were sub-optimal. Chick growth rate was strongly negatively associated with hatching date and worsening weather during the reproductive season could be excluded as explanatory variable for this finding.

Male behaviour over the season in a wild population of the field cricket Gryllus campestris L.

Abstract 1. Cricket model systems have greatly enhanced our knowledge about mate choice and sexual selection. However, no studies exist that take seasonal dynamics into account and that follow individual males over the complete adult stage in the wild. In the present study, all adult field crickets (Gryllus campestris L.) were individually marked and measured in a population in central Germany and their behaviour was followed over their life from May to July 2000.

Natural and sexual selection on male behaviour and morphology, and female choice in a wild field cricket population: spatial, temporal and analytical components

We used multiple regression, path analysis and non-parametric selection surface visualisation to investigate natural and sexual selection and, in addition, cross-sectional female choice statistics to analyse female choice in a wild population of the field cricket Gryllus campestris L. in central Germany. Adults (167 males, 75 females) were individually marked and followed daily over the entire adult stage. Two morphological traits (pronotum width, body condition) and two behavioural traits (burrow occupation time, daily displacement) were measured for each male and used in selection analyses. Individuals mated multiply and male mating success was strongly right skewed with less than 6% of the population achieving 50% of the copulations. In males, analysis of natural selection in terms of lifespan revealed positive directional selection on burrow occupation time and stabilising selection on daily displacement. Analysis of sexual selection in term of mating success showed positive directional selection on pronotum width and lifespan. Path analysis confirmed the close association between natural and sexual selection and illustrated indirect effects of the behavioural variables on mating success via their effect on lifespan. Multiple regression analysis further indicated positive quadratic (disruptive) sexual selection on lifespan but the non-parametric cubic spline regression showed this to be an artefact of the quadratic approach. In fact, lifespan was under “threshold selection” i.e. it was not under selection below a threshold and under positive directional sexual selection above the threshold. A positive correlational selection gradient between lifespan and body condition revealed that a high body condition is advantageous among long-lived males. Female choice statistics showed that females chose large and heavy males in the beginning of the season only and that choosiness decreases with increasing distance to potential alternative mates. Our findings highlight the benefits of combining several analytical methods to uncover selection patterns and to avoid misinterpretations based on single methods.

The role of the male's cerci in copulation and mate guarding in decorated crickets (Gryllodes sigillatus)

Cerci are paired, sensory appendages extending from the terminal abdominal segment of crickets. While the cerci are acutely sensitive to air currents and thereby function in the detection of potential predators, they are also known to play a role in co-ordinating movements of males and females during copulation. The role of the males cerci at four stages of the mating sequence (courtship, copulation, mate guarding and spermatophore removal) was examined by experimentally removing the cerci of male decorated crickets Gryllodes sigillatus and comparing their mating success with that of control males. The mating success of cercectomized males was significantly reduced relative to control males, primarily because of their greater inability to induce females to mount. Even when they succeeded in securing an initial mount, cercectomized males took significantly longer to transfer a spermatophore than did control males. Cercectomy had no influence on the efficacy of post-copulatory mate guarding by males, nor did females discriminate against cercectomized males by removing their spermatophores sooner than those of control males. We conclude that the primary function of the males cerci in sexual interactions in G. sigillatus is to provide tactile stimuli to females that either elicit or guide their mounting response.

Sex recognition in brown skuas: do acoustic signals matter?

Bird vocalisations are often essential for sex recognition, especially in species that show little morphological sex dimorphism. Brown skuas (Catharacta antarctica lonnbergi), which exhibit uniform plumage across both sexes, emit three main calls: the long call, the alarm call and the contact call. We tested the potential for sex recognition in brown skua calls of 42 genetically sexed individuals by analysing 8–12 acoustic parameters in the temporal and frequency domains of each call type. For every call type, we failed to find sex differences in any of the acoustic parameters measured. Stepwise discriminant function analysis (DFA) revealed that sexes cannot be unambiguously classified, with increasing uncertainty of correct classification from contact calls to long calls to alarm calls. Consequently, acoustic signalling is probably not the key mechanism for sex recognition in brown skuas.