Alternative male mating tactics in a cichlid, Pelvicachromis pulcher: a comparison of reproductive effort and success

Pelvicachromis pulcher is a small African cichlid which breeds in holes. Males may either reproduce monogamously (pair males), polygynously (harem males), or be tolerated as helpers in a harem territory (satellite males). These helpers share in defence of the territory against conspecifics, heterospecific competitors and predators. There are two male colour morphs that are fixed for life and are apparently genetically determined. These differ in their potential mating strategy. Red morph males may become harem owners, while yellow morph males may become satellite males, and males of both morphs may alternatively pair up monogamously. We compared the reproductive effort and success of these three male reproductive strategies. Effort was measured as attack rates, time expenditure and the risk of being injured or killed when attacking competitors or predators of three sympatric fish species. Reproductive success was measured by observing how many eggs were fertilized by each male when this was possible, and by using genetic markers. The number of fry surviving to independence of parental care was used as a criterion of success. The reproductive success of harem males was 3.3 times higher than that of pair males and 7 times higher than that of the average satellite male. Dominant satellite males, however, were as successful as monogamous pair males, using the measure of fertilized eggs. To our knowledge, this has not been found previously in any fish species. Both harem and pair males had lower parental defence costs per sired offspring, however, than males using the alternative satellite tactic. Defence effort was significantly related to the risk of injury. Received: 17 January 1996 / Accepted after revision: 9 June 1997     

Threats to Imperiled Freshwater Fauna

Threats to imperiled freshwater fauna in the U.S. were assessed through an experts survey addressing anthropogenic stressors and their sources. Specifically, causes of historic declines and current limits to recovery were identified for 135 imperiled freshwater species of fishes, crayfishes, dragonflies and damselflies, mussels, and amphibians. The survey was designed to identify threats with sufficient specificity to inform resource managers and regulators faced with translating information about predominant biological threats into specific, responsive actions. The findings point to altered sediment loads and nutrient inputs from agricultural nonpoint pollution; interference from exotic species; and altered hydrologic regimes associated with impoundment operations as the three leading threats nationwide, accompanied by many lesser but still significant threats. Variations in threats among regions and among taxa were also evident. Eastern species are most commonly affected by altered sediment loads from agricultural activities, whereas exotic species, habitat removal/damage, and altered hydrologic regimes predominate in the West. Altered sediment loading from agricultural activities and exotic species are dominant problems for both eastern mussels and fishes. However, eastern fishes also appear to be suffering from municipal nonpoint pollution (nutrients and sediments), whereas eastern mussels appear to be more severely affected by altered nutrient impacts from hydroelectric impoundments and agricultural runoff. Our findings suggest that control of nonpoint source pollution associated with agriculture activities should be a very high priority for agricultural producers and governmental support programs. Additonally, the large number of hydropower dams in the U.S. subject to federal re-licensing in coming years suggests a significant opportunity to restore natural hydrologic regimes in the affected rivers.     

The Welfare Bias from Omitting Climatic Variability in Economic Studies of Global Warming

This article analyzes the welfare effects of climatic variability from global warming in a stochastic economic growth model and shows that these may be significant. An empirical analysis indicates that the effects of climate change with variability are greater than the corresponding effects without it. Effects with variability are also shown to be more sensitive to variations in the rate of climate change.     

Population History, Genetic Variability, and Horn Growth in Bighorn Sheep

Bighorn sheep ( Ovis canadensis ) are restricted in distribution and numbers relative to presettlement conditions. Some populations have alledgedly suffered losses of fitness resulting from small, insular populations and a breeding system that reduces effective population size. Large horns in rams, which confer breeding superiority, are absent from some populations, and this absence may result in part from loss of genetic variability. We investigated the relationship among allozyme variability, population history, and horn growth in bighorn sheep from the Rocky Mountains. Heterozygosity was higher for bighorn sheep than has been reported for Dall sheep ( O. dalli ). Heterozygosity and allelic variability were marginally related to effective population size for the proceeding 15 years. Horn growth was significantly higher in more heterozygous than in less heterozygous rams for years 6, 7, and 8 of life. By the end of year 8, more heterozygous rams had 13% higher horn volumes than less heterozygous rams. Most hunting of bighorn sheep involves selective removal of large-horned rams, which we hypothesize may reduce genetic variability of these populations and contribute to losses in fitness.     

Sibling recognition in spiny mice (Acomys cahirinus)

Summary Sibling recognition by spiny mice (Acomys cahirinus) was investigated by housing groups consisting of two pairs of littermates together and recording frequency of dyadic pairing. A total of 136 animals (68 pairs of siblings) were tested in three experiments. Sibling pairs were observed more often than pairings between nonsiblings; however, such preferences were no longer evident if the nonsiblings were exposed to one another prior to testing. Animals made anosmic through zinc sulfate treatment did not differ on their frequencies of sibling vs. nonsibling pairing and showed a higher incidence of group huddling (by all four animals) than did intact controls. Weanling A. cahirinus appear to be able to recognize (i.e., are attracted to) their littermate siblings through olfactory cues, which seems to be a modifiable attraction to odors to which the littermates were exposed rather than an irreversible imprinting-like process.The research project reported herein was supported by grant # 00973 from NICHD     

Inter-male competition for high-quality host-plants: the evolution of protandry in a territorial grasshopper

Summary Males of the desert grasshopper Ligurotettix coquilletti typically eclose 3–5 weeks prior to females. Early-eclosed males experience more female encounters than the later-eclosed individuals. Evidence suggests that the number of encounters may be proportional to male lifetime mating success. Early-eclosed males enjoyed greater adult lifespans, occupied and defended higher quality territories (Larrea shrubs), and tended to be dominant on these shrubs if several males were present. The elevated number of female encounters were not conferred on early-eclosed males by their extended survivorship, but rather by the high quality of their territories, which retained numerous females, and their dominant behavior. We evaluate several female-benefit and male-benefit hypotheses for the evolution of protandry and propose that in L. coquilletti, the phenomenon arose due to male-male competition for female-encounter sites, a mechanism not considered in earlier models. Finally, we discuss several reasons for the high variance in the date of male eclosion.     

Sexual selection on alleles that determine body size in the swordtail Xiphophorus nigrensis

Summary In a natural population, we document changes in the frequencies of alleles influencing body size and size-correlated alternative male reproductive tactics, and we examine the possible role of sexual selection in producing these changes. Male swordtails (Xiphophorus nigrensis, Rio Choy) exhibit three body size classes (small, intermediate, and large) that primarily derive from allelic variation (s, I, L) at the Y-linked pituitary (P) locus. Some XX individuals are male. They are small and can be fathered either by XX or XY males. We compared the frequencies of Y-linked P alleles across two generations in a natural population. There was a significant decrease in the Y-s genotype relative to Y-I and Y-L genotypes. Laboratory experiments suggest that the disadvantage of Y-s resulted, at least in part, from female preference for larger courting males relative to small chasing males. All larger courting males are of the Y-I or Y-L genotypes. Although the frequency of Y-linked P alleles changed across generations, there was no change in the distribution of male body size classes. The stability of the phenotypic distribution across generations, despite changes in P allele frequencies, was maintained by the production of small XX sons by Y-I and Y-L males. Offprint requests to: M.J. Ryan