Dr. Alexandra Schrempf
Evolution, Behaviour & Genetics
Biology I

University of Regensburg
D-93040 Regensburg
Germany

+49 941 943 3001

alexandra.schrempf(at)biologie.uni-regensburg.de

List of publications


Research interests: Sexual selection, aging and reproduction in social insects

Study organisms: Ant species of the genus Cardiocondyla

The genus Cardiocondyla

Cardiocondyla is characterized by a male polymorphism with winged disperser males and wingless fighter males (“ergatoid males”), which engage in fatal fighting over access to the virgin queens eclosing in their natal nest. The convergent loss of winged males in a number of clades and the evolution of mutually tolerant wingless males in a monophylum of single-queen species appear to be derived traits (Heinze et al. 2005). Sexuals mate in the lab within the nests, and the life span of queens is comparatively short (< 1 year), so that the total lifetime reproductive success of queens can be determined.

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Projects:

1) Cooperation between the sexes in the ant genus Cardiocondyla (cooperation with Prof. Dr. Klaus Hartfelder, Ribeirão Preto, Brazil)

Mating partners in promiscuous animals may have opposing interests about the future reproductive performance of the female. Males gain most through forcing it to invest maximally in short-term reproduction, while females often benefit more from re-mating and saving resources for future clutches. This sexual conflict has led to the evolution of male genital structures and seminal fluids, which harm the females, prevent them from re-mating, and / or decrease their life expectancy, and to respective counter-measures in the females.
In species with lifelong pair-bonding, such as social Hymenoptera (bees, ants, wasps), sexual conflict is not expected and sexuals should instead aim at cooperating. In the male-dimorphic ant Cardiocondyla obscurior, mating itself is beneficial for females in that it increases their life spans. Interestingly, mating with winged males has a stronger effect on the life span and reproductive success of queens than mating with wingless males. As males neither provide nuptial gifts nor any other assistance after mating, we hypothesize that seminal fluids play a crucial role. In this project, we focus on the proximate mechanisms of sexual cooperation, e.g. by investigating the composition of seminal fluids transferred by the different types of males during copulation by two-dimensional electrophoresis (DIGE) and representational difference analysis of gene expression in male accessory glands.


2) Multiple mating and sperm competition in the genus Cardiocondyla

As single mating increases the lifespan of Cardiocondyla obscurior ant queens (see above), we study the effect of double mating on female reproductive output and longevity and investigate with the help of genetic markers (microsatellites) whether both males contribute equally to the offspring of the queen. Preliminary results suggest that only sperm of the first male contributes to the female offspring in this polygynous species.
In several monogynous species, multiple mating has been already demonstrated, and in these, sperm competition is expected to occur. Hence, although cooperation between males and females is expected, males may try to hinder females from remating or attempt to somehow outcompete the rival sperm in the females spermatheca. Comparisons of species that experience different levels of sperm competition concerning male traits as e.g. sperm length, sperm viability and the number of sperm transferred during a copulation may help to determine the level of sperm competition and elucidate mechanisms of sperm competition.

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Paternity analysis of several other Cardiocondyla species will show whether all monogynous species are polyandrous and whether on the other hand all polygynous species are monandrous. This might then suggest a genetic background for polyandry in monogynous species (to increase variability).


3) Outbreeding in monogynous Cardiocondyla species

In monogynous Cardiocondyla species with wingless males only, siblings (male and female offspring of the single queen) mate inside the nest, and accordingly, high inbreeding values have been demonstrated (e.g. 83% in C. batesii, Schrempf et al, BES 2005); nevertheless, data suggest that mating between unrelated individuals happen to a certain degree, and in Cardiocondyla elegans, unrelated sexuals have been detected in foreign unrelated nests (Lenoir et al, 2007). We will examine whether this exchange of foreign sexuals can be seen in other monogynous Cardiocondyla species as well and in detail investigate this phenomenon.