Density-dependent sex ratio in Echinomermella matsi (Nematoda), a parasite of the sea urchin Strongylocentrotus droebachiensis
Density-dependent sex ratio in Echinomermella matsi (Nematoda), a parasite of the sea urchin Strongylocentrotus droebachiensis
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DOI：
10.1017/s0031182000065136
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发表时间：
1996-01
期刊：
影响因子：
2.4
通讯作者：
A. Stien;O. Halvorsen;H. P. Leinaas
中科院分区：
文献类型：
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作者：
A. Stien;O. Halvorsen;H. P. Leinaas
摘要我们调查了马氏棘球线虫的70个亚种群的成虫性比。成虫性别比在低成虫强度下偏向雌性优势，在高成虫强度下偏向男性优势。我们假设这是由于性别发育和死亡率的差异，或者女性招募是密度相关的。如果女性的发育和死亡率是男性的几倍，那么在性别发育和死亡率方面存在差异的模型可能会得出观察到的性别比例。两性发育率的巨大差异似乎是不合理的，因为两性的发育率都很低，而且预测的低女性预期寿命不太可能，因为随着女性年龄的增长，男性似乎积累在低于人口数量的人群中。然而，女性人数对密度的依赖得到了以下事实的支持：在有老年女性的低人口中，女性招募人数显著减少。我们还发现，平均雄性长度与拥挤程度呈负相关，从而支持了竞争在马尾松亚种群中的重要性的假说。在低感染强度下的雌性偏向，在雌性招募中的密度依赖，以及E.matsi的分类地位，表明这种线虫的性别可能是由环境决定的。
SUMMARY We investigated the adult sex ratio in 70 infrapopulations of the nematode Echinomermella matsi, a parasite of the green sea urchin Strongylocentrotus droebachiensis. The adult sex ratio was skewed towards female dominance at low adult intensity and towards male dominance at high adult intensity. We hypothesize that this is due to differences between the sexes in development and mortality rates, or that female recruitment is density dependent. A model with differences between the sexes in developmental and mortality rates may develop the observed sex ratios if the female developmental and mortality rates are several times that of the males. A large difference in developmental rates between the sexes appears unreasonable because the developmental rate for both sexes is low, and the predicted low female life-expectancy is unlikely because the males appear to accumulate in infrapopulations as the females age. Density dependence of female numbers is, however, supported by a significantly lower female recruitment in infrapopulations with old females. We also find that the mean male length is negatively related to measures of crowding, thereby supporting the hypothesis that competition is of importance in E. matsi infrapopulations. A female bias at low intensities of infection, a density dependence in female recruitment and the taxonomic position of E. matsi indicate that sex may be environmentally determined in this nematode.