Institute of Evolutionary Biology and Environmental Studies, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland.
BMC Evol Biol. 2011 May 10;11:121. doi: 10.1186/1471-2148-11-121.
Both natural and sexual selection are thought to influence genetic diversity, but the study of the relative importance of these two factors on ecologically-relevant traits has traditionally focused on species with conventional sex-roles, with male-male competition and female-based mate choice. With its high variability and significance in both immune function and olfactory-mediated mate choice, the major histocompatibility complex (MHC/MH) is an ideal system in which to evaluate the relative contributions of these two selective forces to genetic diversity. Intrasexual competition and mate choice are both reversed in sex-role reversed species, and sex-related differences in the detection and use of MH-odor cues are expected to influence the intensity of sexual selection in such species. The seahorse, Hippocampus abdominalis, has an exceptionally highly developed form of male parental care, with female-female competition and male mate choice.
Here, we demonstrate that the sex-role reversed seahorse has a single MH class II beta-chain gene and that the diversity of the seahorse MHIIβ locus and its pattern of variation are comparable to those detected in species with conventional sex roles. Despite the presence of only a single gene copy, intralocus MHIIβ allelic diversity in this species exceeds that observed in species with multiple copies of this locus. The MHIIβ locus of the seahorse exhibits a novel expression domain in the male brood pouch.
The high variation found at the seahorse MHIIβ gene indicates that sex-role reversed species are capable of maintaining the high MHC diversity typical in most vertebrates.Whether such species have evolved the capacity to use MH-odor cues during mate choice is presently being investigated using mate choice experiments. If this possibility can be rejected, such systems would offer an exceptional opportunity to study the effects of natural selection in isolation, providing powerful comparative models for understanding the relative importance of selective factors in shaping patterns of genetic variation.
自然选择和性选择都被认为会影响遗传多样性，但传统上，关于这两个因素对具有传统性别角色的物种的生态相关特征的相对重要性的研究，主要集中在雄性间竞争和基于雌性的配偶选择上。主要组织相容性复合体（MHC/MH）在免疫功能和嗅觉介导的配偶选择中具有高度的可变性和重要性，是评估这两种选择力量对遗传多样性相对贡献的理想系统。性角色反转物种中的种内竞争和配偶选择都发生了反转，并且性别相关的 MH-气味线索的检测和使用差异预计会影响这种物种中性选择的强度。海马，Hippocampus abdominalis，具有一种极其发达的雄性亲代养育形式，存在雌性间竞争和雄性配偶选择。
本文中，我们证明了性角色反转的海马只有一个 MH 类 II β链基因，并且海马 MHIIβ 基因座的多样性及其变异模式与具有传统性别角色的物种中检测到的相似。尽管只有一个基因拷贝，但该物种的 MHIIβ 基因座内等位基因多样性超过了该基因座具有多个拷贝的物种。海马的 MHIIβ 基因座在雄性育儿袋中具有一个新的表达域。
在海马的 MHIIβ 基因中发现的高度变异表明，性角色反转的物种能够维持大多数脊椎动物中典型的 MHC 多样性。目前正在通过配偶选择实验来研究这种物种是否已经进化出在配偶选择过程中使用 MH-气味线索的能力。如果这种可能性可以被否定，那么这些系统将提供一个研究自然选择的独特机会，可以提供有力的比较模型，用于理解选择因素在塑造遗传变异模式方面的相对重要性。
