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The significance of polyandry as a counteraction to selfish genetic elements 博士課程1年 等百合佳

2017/11/22 6:26 に Yurika Hitoshi が投稿
It is known that females of majority of the insects mate multiply, even though theory suggests one or a few matings are sufficient. In terms of individual fitness, this could be explained by the increase of lifetime offspring production (1). Furthermore, polyandry of females may benefit populations by protecting them against extinction caused by a selfish sex-ratio-distorting element. 
Most species carry selfish genetic elements in their genome, which enhance their own transmission relative to the rest of the individual's genome such as P-element in Drosophila melanogaster (2). In Drosophilidae species, Sex Ratio (SR) is a well-known meiotic driving X chromosome which causes the death of all Y-chromosome-bearing sperm during spermatogenesis, which may eventually lead to extinction of the species owing to the lack of males (3). However, the abundance of SR is broadly stable in some species. 
Polyandry may be the key factor reducing the risk of extinction. Since SR-carrying males produce fewer sperms, carrier males could be poor sperm competitors, and hence polyandry may reduce the risk of their offspring inheriting SR. In fact, experimental evolution using Drosophila pseudoobscura demonstrated that polyandry can directly control the spread of SR, whereas monandrous population greatly increased the risk of extinction after 15 generations (4). The cline of polyandry represents an important contributor of the cline in SR in nature in this species as well (5, 6). 
However, recent study discovered that there was no evidence of polyandry in SR- possessing population of Drosophila subobscura (7). SR is persistence for more than 50 years in this population, which indicates that there are factors other than polyandry which could impact the success of SR in the nature as well. 

[References]
1. Arnqvist G & Nilsson T (2000) The evolution of polyandry: multiple mating and female fitness in insects. Animal Behaviour 60:145-164.

2. Kidwell MG & Novy JB (1979) HYBRID DYSGENESIS IN DROSOPHILA-MELANOGASTER - STERILITY RESULTING FROM GONADAL-DYSGENESIS IN THE P-M SYSTEM. Genetics 92(4):1127-1140.

3. Jaenike J (2001) Sex chromosome meiotic drive. Annual Review of Ecology and Systematics 32:25-49.

4. Price TAR, Hurst GDD, & Wedell N (2010) Polyandry Prevents Extinction. Current Biology 20(5):471-475.

5. Price TAR, et al. (2014) Does polyandry control population sex ratio via regulation of a selfish gene? Proceedings of the Royal Society B-Biological Sciences 281(1783).

6. Dyer KA (2012) LOCAL SELECTION UNDERLIES THE GEOGRAPHIC DISTRIBUTION OF SEX-RATIO DRIVE IN DROSOPHILA NEOTESTACEA. Evolution 66(4):973-984.

7. Verspoor RL, Hurst GDD, & Price TAR (2016) The ability to gain matings, not sperm competition, reduces the success of males carrying a selfish genetic element in a fly. Animal Behaviour 115:207-215.
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