Department of Botany and Zoology, Faculty of Sciences, Masaryk University, Brno, Czech Republic.
PLoS One. 2011 Jan 27;6(1):e14603. doi: 10.1371/journal.pone.0014603.
Divergence in trophic niche between the sexes may function to reduce competition between the sexes ("intersexual niche partitioning hypothesis"), or may be result from differential selection among the sexes on maximizing reproductive output ("sexual selection hypothesis"). The latter may lead to higher energy demands in females driven by fecundity selection, while males invest in mate searching. We tested predictions of the two hypotheses underlying intersexual trophic niche partitioning in a natural population of spiders. Zodarion jozefienae spiders specialize on Messor barbarus ants that are polymorphic in body size and hence comprise potential trophic niches for the spider, making this system well-suited to study intersexual trophic niche partitioning.
METHODOLOGY/PRINCIPAL FINDINGS: Comparative analysis of trophic morphology (the chelicerae) and body size of males, females and juveniles demonstrated highly female biased SSD (Sexual Size Dimorphism) in body size, body weight, and in the size of chelicerae, the latter arising from sex-specific growth patterns in trophic morphology. In the field, female spiders actively selected ant sub-castes that were larger than the average prey size, and larger than ants captured by juveniles and males. Female fecundity was highly positively correlated with female body mass, which reflects foraging success during the adult stage. Females in laboratory experiments preferred the large ant sub-castes and displayed higher capture efficiency. In contrast, males occupied a different trophic niche and showed reduced foraging effort and reduced prey capture and feeding efficiency compared with females and juveniles.
CONCLUSIONS/SIGNIFICANCE: Our data indicate that female-biased dimorphism in trophic morphology and body size correlate with sex-specific reproductive strategies. We propose that intersexual trophic niche partitioning is shaped primarily by fecundity selection in females, and results from sex-differences in the route to successful reproduction where females are selected to maximize energy intake and fecundity, while males switch from foraging to invest in mating effort.
两性之间营养生态位的分歧可能有助于减少两性之间的竞争（“两性间生态位分离假说”），也可能是由于两性之间在最大限度地提高繁殖产出方面的差异选择所致（“性选择假说”）。后者可能导致雌性因繁殖选择而产生更高的能量需求，而雄性则投资于寻找配偶。我们在一个蜘蛛自然种群中检验了两性间营养生态位分离的两个假说的预测。Zodarion jozefienae 蜘蛛专门以 Messor barbarus 蚂蚁为食，这些蚂蚁在体型上是多态的，因此构成了蜘蛛潜在的营养生态位，使这个系统非常适合研究两性间营养生态位分离。
方法/主要发现：对雄性、雌性和幼蛛的营养形态（螯肢）和体型进行比较分析，表明体型、体重和螯肢大小存在强烈的雌性偏态性（性二态性），后者源于营养形态的性别特异性生长模式。在野外，雌性蜘蛛积极选择比平均猎物体型大、比幼蛛和雄蛛捕捉到的蚂蚁更大的蚂蚁亚种。雌性蜘蛛的繁殖力与雌性体重呈高度正相关，这反映了成虫阶段的觅食成功。在实验室实验中，雌性蜘蛛更喜欢大型蚂蚁亚种，表现出更高的捕捉效率。相比之下，雄性蜘蛛占据了不同的营养生态位，与雌性和幼蛛相比，雄性蜘蛛的觅食努力、猎物捕捉和摄食效率都降低了。
结论/意义：我们的数据表明，营养形态和体型的雌性偏态二态性与雌性特有的繁殖策略相关。我们提出，两性间营养生态位分离主要是由雌性的繁殖选择塑造的，是雌性为了最大限度地增加能量摄入和繁殖力而选择，而雄性则从觅食转向投资交配努力的结果。
