Cooperation between the sexes in the ant genus Cardiocondyla
In numerous animal species the interests of males and females in reproductive investment diverge. Males are usually more interested in increasing the short-term fecundity of the female, whereas females would better save some energy for future mating and reproduction (Parker & Partridge 1979). Thus, sexual conflict leads to a perpetual antagonistic coevolution between the two sexes (Rice 1996 & 2000). In particular, traits relevant for reproduction are affected and the adaptation of one sex is followed by a counter-adaptation of the other sex. Thus, traits may evolve that are beneficial for one sex but harmful for the other. For instance, males of the model organism Drosophila melanogaster have evolved accessory gland proteins (ACPs) - components of the seminal fluid, which are transferred during mating- that not only increase the short-term fecundity of the females but also harm them by reducing the lifespan of mated females relative to that of virgins (Chapman et al. 1995 & 1996)
A very different life-history can be found in social insects (wasps, bees, ants). They usually engage in life-long pair-bonding. Queens normally mate only during a short time-range early in their life and do not remate later. The sperm of one or a few matings is stored in the spermatheca for the rest of their life. In most social insect species (except termites), males die shortly after mating and do not assist the queens in founding a new colony. The male`s genes persist just as stored sperm. Because of haplo-diploidy, only daughters will have the male`s genes, and as workers play only a minor role in reproduction, only young queens transmit the male`s genes to the next generation. If a queen has to found a new colony on her own, she will first produce workers. Sexuals will be reared at the earliest only several months after successful colony establishment. Due to this “late reproduction” it is of great importance to the male that the queen lives long enough to produce common, female sexual offspring (Hölldobler & Wilson, 1990; Bourke & Franks 1995).
Because of this special life-cycle of social insects, the occurrence of sexual conflict is not very likely. One would therefore expect “sexual cooperation”, in a way that the male supports the female posthumously to found a new colony.
The study species:
The ant genus Cardiocondyla is a good model organism to study “sexual cooperation” in social insects. In the polygynous species Cardiocondyla obscurior, two different male morphs occur. Under normal environmental conditions, wingless, ergatoid males are present in the colony. They are produced continuously, stay life-long inside the nest and mate throughout their whole life as they have an ongoing spermatogenesis. When environmental conditions deteriorate, winged ant males - as are typical for other ant species - appear in large numbers. They disperse after several days and are thought to mate outside to ensure the propagation of the “colony’s genes” via outbreeding. Under bad environmental conditions, young queens presumably also leave their natal nests and found new colonies on their own, without the help of workers. A recent study showed that queens, mated with a winged male, live longer than queens, which mated with an ergatoid male.
a) Ergatoid male of Cardiocondyla obscurior
b) Accessory glands and testes of an ergatoid male
Questions and methods:
a) Is the protein composition of the male accessory glands of the two different male morphs different from each other?
Fluorescence- labeled 2D-SDS-PAGE (2 dimensional-SDS-polyacrylamide gel electrophoresis)
b) Are genes in the accessory glands of the two male morphs differentially expressed?
RDA (representational difference analysis)
c) Are queens treated differently by workers, depending on whether they have mated with an ergatoid or a winged male?
d) Can the stronger life-prolonging effect of winged males also be seen in other Cardiocondyla species?
For scanning and evaluation of the fluorescence-labeled Gels I cooperate with the Institute of Functional Genomics (University of Regensburg)
For the representational difference analysis I cooperate with Prof. Dr. Klaus Hartfelder, Ribeirão Preto, Brazil
a) University of São Paulo, Campus of Ribeirão preto
b) A very tall Ficus elastica
c) Rio Paranapanema
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2. Chapman T, Liddle LF, Kalb JM, Wolfner MF, Partridge L. Cost of mating in Drosophila melanogaster females is mediated by male accessory gland products. Nature 1995;373:241-244.
3. Chapman T, Partridge L. Sexual conflict as fuel for evolution. Nature 1996;381:189-190.
4. Hölldobler B, Wilson EO. The ants. Cambridge, Mass.: Havard University Press, 1990.
5. Parker GA, Partridge L. Sexual conflict and speciation. Philosophical Transactions of the Royal Society B: Biological Sciences 1998;353:261-274.
6. Rice WR. Sexually antagonistic male adaption triggered by experimental arrest of female evolution. Nature 1996;381:232-234.
7. Rice WR. Dangerous liaisons. Proceedings of the National Academy of Scienes USA 2000;97:12953-12955.