Julie Stahlhut
Posts: 46
Joined: July 2005
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Alan wrote:
| Quote | | BTW would lack of vulnerability to PI in bees and wasps due to (presumably) haplo-diploid sex determination have had an effect on its evolutionary appearance or development? |
This is something that's not well-characterized yet, and in fact it's a path I'd like to pursue. It turns out that not all haplodiploid sex determination systems are alike; the underlying pathways differ, and there seem to have been multiple and diverse responses to selection on sex determination mechanisms.
Brief oversimplification: Most bees, ants, and true wasps have a single sex-determining locus (no sex chromosomes) with many alleles. Haploids are male, and diploids are almost always heterozygous at the sex locus and become female. Homozygous diploids develop as males, and these diploid males are usually inviable or infertile. This is called single-locus complementary sex determination, or sl-CSD (or just CSD). Just a few years ago, the sex locus of the honeybee was definitively identified by Martin Beye and co-workers.
Since inbreeding produces more homozygotes, homozygotes become diploid males, and diploid males tend not to reproduce, we'd predict:
1. Species with CSD should avoid inbreeding.
Support: Most species with CSD have inbreeding avoidance behaviors. For example, many bees and ants have "nuptial flights" and mate far from their natal nests. Many solitary wasp species also disperse before mating.
2. Species whose life histories promote inbreeding should have a different sex-determination system.
Support: Parasitoid wasps that tend to mate with siblings after emerging from a host usually don't have CSD; breeding experiments support this. The overall pattern, when mapped onto hymenopteran phylogeny, suggests ancestral CSD that was secondarily lost in many parasitoid lineages. However, the latter is still a topic for conjecture, because we don't have enough information to be sure.
My own dissertation research, BTW, uncovered a bizarre exception. One solitary, predatory wasp common in the U.S. has CSD (breeding experiments clinched this), often mates with siblings (about two-thirds of matings in the population I studied, based on genetic data), produces diploid males under inbreeding (confirmed by genetic markers) -- and these diploid males are fertile, fathering normal daughters (confirmed by breeding experiments and genetic markers). So, they've "found" another way around the CSD vs. inbreeding dilemma!
3. Only those hymenopterans that lack CSD should have Wolbachia-induced parthenogenesis (PI), because otherwise the gamete duplication process would produce diploid males, not daughters.
Support: To date, PI has been found only in non-CSD, parasitoid Hymenoptera. However, this doesn't rule out different, unknown mechanisms for parthenogenesis induction in CSD species; we just haven't really looked yet. It also doesn't rule out male-killing or cytoplasmic incompatibility; the latter (CI) may yet turn out to be a considerable player in hymenopteran biology.
| Quote | | You should contact Dr Elsberry about doing a guest contribution on PT. |
I'll put that on my list of things to do. :-) Gotta get a manuscript revised first, but it would be fun to do a Wolbachia essay!
Dean wrote:
| Quote | | Your enthusiasm for the subject shines through - isn't nature great? |
Well, y'know, I just love my bugs! Started getting interested at age 7, but didn't do anything about it for entirely too long (finally got my Ph.D. at age 46). I try to do my best to get younger people started on what they like rather than what they think they're supposed to like.
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