Body size preferences in the pot-bellied seahorse <Emphasis Type="Italic">Hippocampus abdominalis:</Emphasis> choosy males and indiscriminate females

Male seahorses (genus Hippocampus) provide all post-fertilization parental care, yet despite high levels of paternal investment, these species have long been thought to have conventional sex roles, with female mate choice and male–male competition. Recent studies of the pot-bellied seahorse (Hippocampus abdominalis) have shown that sex-role reversal occurs in high-density female-biased populations, indicating that male mating preferences may lead to sexual selection on females in this species. Egg size, egg number, and offspring size all correlate positively with female body size in Hippocampus, and by choosing large mating partners, male seahorses may increase their reproductive success. While male brood size is also positively correlated with body size, small H. abdominalis males can carry exceptionally large broods, suggesting that the fecundity benefits of female preference for large partners may be limited. We investigated the importance of body size in reproductive decisions of H. abdominalis, presenting focal individuals of both sexes with potential mating partners of different sizes. Mating preferences were quantified in terms of time spent courting each potential partner. Male seahorses were highly active throughout the mate-choice trials and showed a clear behavioral preference for large partners, while females showed significantly lower levels of activity and equivocal mating preferences. The strong male preferences for large females demonstrated here suggest that sexual selection may act strongly on female body size in wild populations of H. abdominalis, consistent with predictions on the importance of female body size for reproductive output in this species. An erratum to this article can be found at     

Size-assorted fish shoals and the majority's choice

Similarity among group members may serve as a defence against visually hunting predators that preferentially attack individuals who are phenotypically different from the group majority. The presence of such odd individuals in an otherwise homogeneous group may, however, increase the vulnerability of the other group members as well. Individuals might thus be expected to form uniform groups in order to decrease predation risk, not only in trying to avoid being odd in a group, but also when attempting to avoid being accompanied by odd individuals. This hypothesis was tested with small and large three-spined sticklebacks, Gasterosteus aculeatus. Focal fish were offered the choice between a shoal consisting of conspecifics that were all similar in body length to the focal fish (matching shoal) and a shoal in which one or a few individuals differed in body length from the focal fish (non-matching shoal). In the control experiment, all individuals in the non-matching shoal differed in size from the focal fish. The control confirmed that individuals preferably joined the matching shoal when the alternative option was to be odd in another one. However, when the alternative for size-assortative shoaling was to belong to the majority in a mixed shoal, the shoal choice of individuals appeared on average to be random. Visual contact with a live pike, Esox lucius, did not affect the shoal choice pattern. Furthermore, despite the frequency-dependent nature of the oddity effect, varying the number of odd individuals in the non-matching shoal did not have a significant effect on individual's shoaling decisions. These results suggest that size-assortativeness in fish shoals is not a result of individuals avoiding being among the majority in a mixed group. Received: 2 September 1998 / Received in revised form: 12 May 1999 / Accepted: 29 May 1999     

Mate choice among sympatric fur seals: female preference for conphenotypic males

When closely related species breed in sympatry, and where hybrids have lower fitness, reinforcement theory predicts that selection should favour mechanisms that reduce the probability of interspecific matings. If this situation arises among species that exhibit resource defence polygyny where males and females of different species reside in the same territories, there may be some conflict between mate choice based on territory-holding ability (sexual selection) and mate choice for correct species. We investigated this in a population of fur seals where three species are sympatric and where some females breed in the territories of heterospecific males, and where interspecific matings and hybrid pups are observed. The territorial status of males and the birthing sites of females were determined during daily observations, as were the movements of males and females, the location of matings and mating partners. DNA extracted from skin samples was used to determine paternities using DNA fingerprinting and the mtDNA genotype of individuals. Individuals were also classed on the basis of species-typical phenotype. We found that extra-territory inseminations (ETIs) were significantly more prevalent (67%) when territorial males and resident females were of different phenotype than when of similar phenotype (27%), but mtDNA genotype had no effect on the rate of ETIs. ETIs were probably by males with the same phenotype, as pups born to these females in the following season had the same phenotype as their mothers, suggesting they were not hybrids. These results suggest that within the resource defence polygynous mating system of these sympatric fur seals, female mate choice is more influenced by male phenotype than genotype. Contrary to our predictions, our study indicates that potential conflict between mate choice based on sexual selection and species recognition is unlikely, because females have some capacity to discriminate between males both within and between species on phenotypic traits additional to those under sexual selection. Although at least 25% of the pups born in this study were hybrid, this study can only support reinforcement theory if hybrids have reduced fitness. The fitness of hybrids among the species studied is currently unknown. Received: 19 January 1998 / Accepted after revision: 12 September 1998     

Optimal nonpoint source pollution control strategies for a reservoir watershed in Taiwan

The purpose of this study is to develop a model for optimal nonpoint source pollution control for the Fei-Tsui Reservoir watershed in Northern Taiwan. Several structural best management practices (BMPs) are selected to treat stormwater runoff. The complete model consists of two interacting components: an optimization model based on discrete differential dynamic programming (DDDP) and a zero-dimensional reservoir water quality model. A predefined procedure is used to locate suitable sites for construction of various selected BMPs in the watershed. In the optimization model, the objective function is to find the best combination of BMP type and placement, which minimizes the total construction and operation, maintenance, and repair (OMR) costs of the BMPs. The constraints are the water quality standards for total phosphorus (TP) and total suspended solids (TSS) concentrations in the reservoir. A zero-dimensional reservoir water quality model of the Vollenweider type is embedded in the optimization framework to simulate pollutant concentrations in Fei-Tsui Reservoir. The resulting optimal cost and benefit of water quality improvement are depicted by the model-derived trade-off curves. The modeling framework developed in the present study could be used as an efficient tool for planning a watershed-wide implementation of BMPs for mitigating stormwater pollution impact on the receiving water bodies.     

基于选择实验方法的北京市空气质量价值评估

科学地评估空气质量的经济价值是政府制定空气污染治理政策的必要前提。近年来选择实验方法逐渐兴起,并被研究者广泛应用于环境价值评估。与其他陈述偏好方法相比,选择实验的一个优势是其具有更高的外部效度。选择实验方法在国内的应用研究尚处在起步阶段。本研究分别在2015年和2016年对北京市居民开展了两次基于选择实验方法的网络调查,在调查数据的基础上采用随机参数Logit和广义多元Logit模型分析了北京市居民对空气质量的偏好,并据此估算了空气质量价值。根据2015年样本的估算结果,雾霾天气(PM_(2.5)超标)和沙尘天气(PM_(10)超标)对北京市居民的平均边际价值分别为6.32元/d和2.69元/d;根据2016年样本的估算结果,两个价值分别为7.72元/d和2.81元/d。上述估算结果在两次调查样本中基本稳定,而且,在多种模型设定下都具有较强的稳健性,与近年来的同类研究结果基本一致。以2016年样本的估算结果为基础,2015年北京市雾霾天气和沙尘天气引起的价值损失分别为239.61亿元和45.13亿元,占北京市当年GDP总量的1.04%和0.20%。进一步研究发现,北京市2015年和2016年空气质量改善的价值均低于北京市政府同年用于治理空气污染投入的财政资金总量,说明资金使用效率有待进一步提高;此外,虽然空气质量对高收入居民具有更高的价值,但是,以收入水平为指标设计的累进税率并不比固定税率更优。     

Major histocompatibility complex and mate choice in a monogamous rodent

A growing number of studies indicate that females can increase the viability of their offspring by gaining direct benefits such as parental care or genetic advantages through selective mating with certain males. Among the best candidates for the genetic basis of mate choice in vertebrates are the genes of the major histocompatibility complex (MHC) because these highly polymorphic genes may increase offspring viability and provide direct cues for mate choice. A free-ranging, pair-living rodent was used as an example to investigate MHC-dependent mate choice in an obligate monogamous species, the Malagasy giant jumping rat Hypogeomys antimena. Two possible mechanisms of mate choice were tested. First, mate choice may occur to increase the heterozygosity of MHC genes in the progeny and, second, mates might choose each other according to the degree of dissimilarity of their functional MHC DRB (exon 2) proteins in order to maximise the allelic divergence in their offspring. Analyses of 65 Hypogeomys couples failed to confirm associations of mating patterns with the MHC genotype to increase heterozygosity or MHC allelic divergence in the progeny. Also, no evidence for mechanisms to increase the allelic divergence was found in sex-specific analyses where a male or female, respectively, migrated to and was accepted by a territory and burrow holder of the opposite sex. However, the frequency distribution of 0, 1 or 2 new alleles potentially available for the progeny differed significantly when a new male was chosen by a territory-holding female. In contrast to current models, genetically similar instead of dissimilar mates seem to be the preferred choice. This is the first study investigating the role of the MHC in mate selection in an obligate monogamous rodent.Communicated by G. Wilkinson     

An application of economic choice experiments to a traditional land use—deer hunting and landscape change in the Scottish Highlands

Stalking (deer hunting) is an important land use and activity in the Scottish Highlands, and deer managers have traditionally maintained large numbers of female deer in order to supply a guaranteed number of stags for stalking. Unfortunately, grazing by large numbers of deer conflicts with environmental objectives that are seeking to improve upland habitats and increase the area of native Caledonian Pine forest. This study uses a multi-attribute choice experimental approach to quantify the various characteristics of the stalking experience to determine the value that amateur stalkers attach to the stag numbers, the landscape and other attibutes. Unlike previous applications of stated preference, a large proportion (one-third) of a full factorial design is used to present stalkers with different alternative stalking packages within a postal survey. The results indicate a way forward that could be agreeable to both deer managers and conservationists.