Mating competition and intergroup transfer of males in Tibetan macaques (Macaca thibetana) at Mt. Emei,China

In five groups of seasonally provisioned Tibetan macaques (Macaca thibetana) at Mt. Emei, males were sampled for wounds as an indicator of their competition for females during about 80 days in the 1987 mating season. Quantitative data on intergroup transfer were collected in a period between June 1986 and December 1987. The young adult (YA) males, the most active age-class in mating activity and intergroup transfer, received most of the wounds. Wounds tended to appear more in the front of body for YA and subadults (SA) than they did for middle-old aged (MO) males. This implies that some of the MO males were more active and aggressive in the fights. During the 1.5 year period, 5/6 of the YA and 5/17 of the MO males made intergroup shifts. Although YA males faced a high risk of receiving wounds at transfer, they usually rose in rank. On the other hand, the MO males transferred more smoothly but dropped in rank. The peripheral SA males, which rarely emigrated in the population, were an active component in determining the wounding rate, and the rate and direction of male migration. Three SA immigrants died of severe attacks made by resident males in 1988 and 1991. Adult sex ratios and their variations were considerably reduced with male nonrandom shifts and better conservation of the population.     

An unusual sex-determination system in South American field mice (Genus Akodon): the role of mutation, selection, and meiotic drive in maintaining XY females

The mechanism of sex determination in mammals appears highly conserved: the presence of a Y chromosome triggers the male developmental pathway, whereas the absence of a Y chromosome results in a default female phenotype. However, if the Y chromosome fails to initiate the male pathway (referred to as Y*), XY* females can result, as is the case in several species of South American field mice (genus Akodon). The breeding genetics in this system inherently select against the Y* chromosome such that the frequency of XY* females should decrease rapidly to very low frequencies. However, in natural populations of Akodon, XY* females persist at substantial frequencies; for example, 10% of females are XY* in A. azarae and 30% in A. boliviensis. We develop a mathematical model that considers the potential roles of three evolutionary forces in maintaining XY* females: Y-to-Y* chromosome transitions (mutation), chromosome segregation distortion (meiotic drive), and differential fecundity (selection). We then test the predictions of our model using data from breeding colonies of A. azarae. We conclude that any single force is inadequate to maintain XY* females. However, a combination of segregation bias of the male and female Y chromosomes during spermatogenesis/oogenesis and increased fecundity in XY* females could account for the observed frequencies of XY* females.     

Adult diet affects lifespan and reproduction of the fruit‐feeding butterfly Charaxes fulvescens

Fruit‐feeding butterflies are among the longest lived Lepidoptera. While the use of pollen‐derived amino acids by Heliconius butterflies has been interpreted as important for the evolution of extended lifespans, very little is known about the life‐history consequences of frugivory. This issue is addressed by investigating effects of four adult diets (sugar, sugar with amino acids, banana, and moistened banana) on lifespan and reproduction in the fruit‐feeding butterfly Charaxes fulvescens Aurivillius (Lepidoptera: Nymphalidae). Female butterflies were collected from Kibale National Park, Uganda, and kept individually in cages near their natural habitat and data were collected on lifespan, oviposition, and hatching of eggs. Lifespan in captivity was longer for the sugar and the amino acid cohort, than for the banana cohorts. The longitudinal pattern of oviposition was erratic, with many days without oviposition and few periods with high numbers of eggs laid. Butterflies typically did not lay eggs during their 1st week in captivity and the length of the period between capture and first reproduction was significantly shorter for butterflies fed moistened banana. The length of the reproduction period (first reproduction–last reproduction in captivity) and the reproduction rate (total number of eggs/length of the reproduction period) did not differ significantly between the diet treatments. Those fed with amino acid and moistened banana had significantly higher egg hatchability than those fed with sugar and banana. We found no evidence for a lifespan cost of reproduction. Our results show that (1) female C. fulvescens can use amino acids in their diet for laying fertile eggs, (2) more wing‐wear does correlate with lower survival in captivity (indicating aging in the wild), but not with intensity of reproduction (providing no evidence for reproductive aging), and (3) fruit‐feeding butterflies may be dietary restricted in the field.     

Progesterone modulates aggression in sex-role reversed female African black coucals

Testosterone is assumed to be the key hormone related to resource-defence aggression. While this role has been confirmed mostly in the context of reproduction in male vertebrates, the effect of testosterone on the expression of resource-defence aggression in female vertebrates is not so well established. Furthermore, laboratory work suggests that progesterone inhibits aggressive behaviour in females. In this study, we investigated the hormonal changes underlying territorial aggression in free-living female African black coucals, Centropus grillii (Aves; Cuculidae). Females of this sex-role reversed polyandrous bird species should be particularly prone to be affected by testosterone because they aggressively defend territories similar to males of other species. We show, however, that territorial aggression in female black coucals is modulated by progesterone. After aggressive territorial challenges female black coucals expressed lower levels of progesterone than unchallenged territorial females and females without territories, suggesting that progesterone may suppress territorial aggression and is downregulated during aggressive encounters. Indeed, females treated with physiological concentrations of progesterone were less aggressive than females with placebo implants. This is one of the first demonstrations of a corresponding hormone-behaviour interaction under challenged and experimental conditions in free-living females. We anticipate that our observation in a sex-role reversed species may provide a more general mechanism, by which progesterone--in interaction with testosterone--may regulate resource-defence aggression in female vertebrates.     

Reduction of inbreeding in commercial females by rotational mating with several sire lines

A mating system to reduce the inbreeding of commercial females in the lower level was examined theoretically, assuming a hierarchical breed structure, in which favorable genes are accumulated in the upper level by artificial selection and the achieved genetic progress is transferred to the lower level through migration of males. The mating system examined was rotational mating with several closed sire lines in the upper level. Using the group coancestry theory, we derived recurrence equations for the inbreeding coefficient of the commercial females. The asymptotic inbreeding coefficient was also derived. Numerical computations showed that the critical factor for determining the inbreeding is the number of sire lines, and that the size of each sire line has a marginal effect. If four or five sire lines were available, rotational mating was found to be quite an effective system to reduce the short- and long-term inbreeding of the commercial females, irrespective of the effective size of each sire line. Oscillation of the inbreeding coefficient under rotational mating with initially related sire lines could be minimized by avoiding the consecutive use of highly related lines. Extensions and perspectives of the system are discussed in relation to practical application.     

Polymorphism in stem females and successive parthenogenetic generations in Brachionus calyciflorus Pallas

We have described the polymorphism in the hatchlings of resting eggs and the morphological variations between the stem females hatched from resting eggs and their successive parthenogenetic generations in the rotifer Brachionus calyciflorus. We hatched resting eggs of B. calyciflorus in two different culture mediums: unconditioned medium (IOM) and Asplanchna-conditioned (ACM). The hatching rate of resting eggs in IOM and ACM were 32.5% and 28.5%, respectively, and showed no significant difference. Stem females hatching from these resting eggs had three morphotypes (unspined, single short-spined, and two short-spined) and over 80% of these females were spineless ones. Moreover, the frequency of each morphotype stem females showed similar tendency in IOM and ACM. The production of a variety of morphotypes among stem mothers—rather than all unspined as has been previously reported for this species—may be regarded as a form of bet-hedging in this population of B. calyciflorus. Phenotypic changes in morphology between the stem females hatched from resting eggs and their successive parthenogenetic generations in B. calyciflorus were found. The possible mechanisms, responsible for high proportion of spineless phenotype at early generations from resting eggs and increased spined phenotype in successive parthenogenetic generations, were discussed in the article.     

An integrative mating system assessment of a nonmodel,economically important Pacific rockfish (Sebastes melanops) reveals nonterritorial polygamy and conservation implications for a large species flock

Characterizing the mating systems of long‐lived, economically important Pacific rockfishes comprising the viviparous Sebastes species flock is crucial for their conservation. However, direct assignment of mating success to sires is precluded by open, offshore populations and high female fecundity. We addressed this challenge by integrating paternity‐assigned mating success of females with the adult sex ratio (ASR) of the population, male evolutionary responses to receptive females, and reproductive life history traits—in the framework of sexual selection theory—to assess the mating system of Sebastes melanops. Microsatellite parentage analysis of 17 pregnant females, 1,256 of their progeny, and 106 adults from the population yielded one to four sires per brood, a mean of two sires, and a female mate frequency distribution with a truncated normal (random) pattern. The 11 multiple paternity broods all contained higher median allele richness than the six single paternity broods (Wilcoxon test: W = 0, p < .001), despite similar levels of average heterozygosity. By sampling sperm and alleles from different males, polyandrous females gain opportunities to enhance their sperm supply and to lower the cost of mating with genetically incompatible males through reproductive compensation. A mean of two mates per mated female with a variance of one, an ASR = 1.2 females per male, and the expected population mean of 2.4 mates for mated males (and the estimated 35 unavailable sires), fits polygamous male mate frequency distributions that distinguish polygynandry and polyandrogyny mating systems, that is, variations of polygamy, but not polyandry. Inference for polygamy is consistent with weak premating sexual selection on males, expected in mid‐water, schooling S. melanops, owing to polyandrous mating, moderately aggregated receptive females, an even ASR, and no territories and nests used for reproduction. Each of these characteristics facilitates more mating males and erodes conspicuous sexual dimorphism. Evaluation of male evolutionary responses of demersal congeners that express reproductively territorial behavior revealed they have more potential mechanisms for producing premating sexual selection, greater variation in reproductive success, and a reduced breeding effective population size of adults and annual effective size of a cohort, compared to S. melanops modeled with two mates per adult. Such divergence in behavior and mating system by territorial species may differentially lower their per capita birth rates, subsequent population growth, and slow their recovery from exploitation.     

Diapause in copepods (Crustacea) from ephemeral habitats with different hydroperiods in Everglades National Park (Florida,U.S.A.)

Water management practices in the Everglades have severely stressed the natural system, particularly by reducing the hydroperiods of much of the region. During the dry season of 1999, we investigated the influence of hydroperiod on the species composition and dormancy patterns of freshwater copepod communities in seasonal wetlands of Everglades National Park, Florida, U.S.A. The habitats were characterized by an annual dry season, from December through June. We sampled at two locations: the Long Pine Key area of the Rocky Glades region (short hydroperiod, ca. 4–5 months), and western Taylor Slough (intermediate hydroperiod, ca. 8–10 months). Both areas have experienced a reduction in natural hydroperiods and an increase in the frequency of dry-down. We collected weekly plankton samples from Rocky Glades solution holes to assess the potential species pool of copepods. To document the taxa capable of surviving dry-down by resting, we performed three immersion trials in which we rehydrated, in laboratory aquaria, sediment patches from solution holes and surface soils from all stations. Only a subset of the planktonic species collected emerged from the dried sediments. The cyclopoids Microcyclops rubellus and Paracyclops poppei were dominant. This is the first record of diapause for P. poppei. Species distributions from the different hydroperiod soil patches indicated that more diapausing species occurred at the sites that dried for shorter periods. Emerging individuals of M. rubellus and P. poppei were mainly ovigerous females, demonstrating a resting strategy seldom before recorded. The cyclopoid Diacyclops nearcticushad not been previously reported to diapause, but they emerged from the dried sediments in our trials. Our collections included six new records for Florida: Diacyclops nearcticus, Megacyclops latipes, Orthocyclops modestus, Elaphoidella marjoryae, Bryocamptus sp. and Bryocamptuscf. newyorkensis. Paracyclops poppei, Macrocyclops fuscus and Arctodiaptomus floridanus are new records for Everglades National Park. Clearly, diapause is an important strategy for the persistence of copepods in short-hydroperiod wetlands. The duration of the dry period appears to be inversely related to the number of species that emerge from diapause.     

VARIATION IN ENVIRONMENTAL AND GENOTYPIC SEX-DETERMINING MECHANISMS ACROSS A LATITUDINAL GRADIENT IN THE FISH,MENIDIA MENIDIA

Models of environmental sex determination (ESD) usually assume that genetic influences on sex are polygenic, but the validity of this (or any other) form of genotype-environment interaction is virtually unknown. In the Atlantic silverside, Menidia menidia, sex is determined by an interaction between temperature and genotype and the response of sex ratio to temperature differs among populations from different latitudes. We examined the genetic basis of this pattern by measuring among family variation in the proportion of females, F/(F + M), within and among high (21°C) and low (15°C) temperatures for two populations: one from Nova Scotia (NS) where the level of ESD is low, and another from South Carolina (SC) where the level of ESD is high. In NS fish, temperature had a significant influence on sex ratio in only 1 of 23 families. The distribution of the fraction of females within temperatures for families from NS was highly heterogeneous and tended to fall into distinct classes (0.0, 0.25, 0.5, 1.0) like that expected from Mendelian segregation of a major sex factor(s). In contrast, temperature had a highly significant influence on sex ratio in all SC families examined (N = 24). Family sex ratios within temperatures were highly heterogeneous and, at least at 15°C, did not conform to simple Mendelian ratios. At 21°C, the proportion of females in most SC families was near zero and so the underlying sex tendencies of different families could not be discerned. Based on a previous study, mid-latitude fish appear to have an intermediate form of sex determination: simple Mendelian sex-ratio patterns exist and there is a moderate thermal influence on sex ratio in most but not all families. We suggest that sex determination in M. menidia is controlled by an interaction between major genetic factors, polygenic factors, and temperature and that the relative importance of each component differs with latitude. High latitude populations appear to have evolved a major sex-determining factor(s) that overrides the effect of temperature, and this factor(s) is lacking in low latitude populations.