Reproductive biology and relative male and female fitness in a trioecious cactus,Pachycereus pringlei (Cactaceae)

We describe the breeding system of an autotetraploid trioecious cactus, Pachycereus pringlei, provide estimates of the fitnesses of males and females relative to that of hermaphrodites, and discuss the role played by pollinators in the maintenance of three sexual morphs. Relatively high frequencies of females (45%) and males (26%) exist in coastal desert populations around Bahia Kino, Sonora, Mexico. They differ from hermaphrodites in flower size (females only), initiation of the flowering season, number of flowers produced per night and per season, sucrose content of nectar, and, in females, number of fruits produced per season under open pollination and in response to hand-pollination. Major similarities between the sex classes include overall plant size, nectar volume per flower, percent fruit set in open-pollinated flowers of females and hermaphrodites, seed mass and number of seeds per fruit, and pollen mass per flower in males and hermaphrodites. Hermaphrodites are self-compatible, and the selfing rate is high (65%). Levels of inbreeding depression in selfed fruits and seeds appear to be low. Fruit set is strongly pollinator-dependent in females but much less so in hermaphrodites. Relative fitness of males and females, as measured by annual production of pollen or seeds, is at least 1.5 times higher than that of the corresponding sex function in hermaphrodites. Given the high selfing rate and apparent lack of inbreeding depression, these fitness differences are insufficient to explain the occurrence of trioecy in this species.     

Queen size mediates queen survival and colony fitness in harvester ants

Abstract We examined the effect of queen size on the probability of new colony establishment in the ant Pogonomyrmex occidentalis. Large queens are significantly more likely to survive than small queens through the initial stages of colony founding. These differences in individual fitness correlates have corresponding effects on colony fitness. In species in which individual queens vary in fitness, sexual allocation ratios should incorporate the individual fitness functions.     

Beyond lifetime reproductive success: the posthumous reproductive dynamics of male Trinidadian guppies

In semelparous populations, dormant germ banks (e.g. seeds) have been proposed as important in maintaining genotypes that are adaptive at different times in fluctuating environments. Such hidden storage of genetic diversity need not be exclusive to dormant banks. Genotype diversity may be preserved in many iteroparous animals through sperm-storage mechanisms in females. This allows males to reproduce posthumously and increase the effective sizes of seemingly female-biased populations. Although long-term sperm storage has been demonstrated in many organisms, the understanding of its importance in the wild is very poor. We here show the prevalence of male posthumous reproduction in wild Trinidadian guppies, through the combination of mark–recapture and pedigree analyses of a multigenerational individual-based dataset. A significant proportion of the reproductive population consisted of dead males, who could conceive up to 10 months after death (the maximum allowed by the length of the dataset), which is more than twice the estimated generation time. Demographic analysis shows that the fecundity of dead males can play an important role in population growth and selection.     

Lifespan in male ants linked to mating syndrome

Male ants have long been thought to leave the nest, swarm, mate and die in quick succession (male aggregation syndrome). However, the ancestors of the ants likely used female calling, where females advertise with pheromones for longer lived and presumably free living males. In this study, male lifespan was compared in four species from a Panama rain forest. Males of two species with aggregation syndrome (Atta colombica and Azteca sp.) lived only days after collection at a light trap, and their lifespan failed to increase when supplied sugar water ad libitum. In contrast, two species with female calling syndrome (Ectatomma ruidum and Paraponera clavata) lived up to 116 days when fed. These results link male lifespan to mating systems, and provide a framework to examine variation in how ant colonies invest in males.     

Relative fitness of aphids: effects of plant quality and ants

We investigated the response of four species of aphids ( Metopeurum fuscoviride , Brachycaudus cardui , Aphis fabae , and Macrosiphoniella tanacetaria ) on tansy ( Tanacetum vulgare ) to plant quality and attendance by an ant, Lasius niger . The aphids experienced one of four different environments for two consecutive generations. Ant-attendance significantly affected the time needed to reach maximum fecundity only in Me. fuscoviride and plant quality in Me. fuscoviride and B. cardui . Maximum daily fecundity was positively affected by plant quality and the magnitude of the effect was inversely associated with the degree of myrmecophily. Ant-attendance had a positive effect on maximum fecundity only in the obligate myrmecophile, Me. fuscoviride . The intrinsic rate of population increase, r _m, on high quality plants, was lowest for the obligate myrmecophile, intermediate for the facultative myrmecophiles and highest for the unattended species. On high quality plants the fitness of Me. fuscoviride was more adversely affected by the developmental stage of the plant and absence of ants than that of A. fabae or Ma. tanacetaria , which were able to maintain a high relative fitness in all the environments. The implications for aphids experiencing different degrees of ant-attendance and seasonal changes in plant quality are discussed.     

Inbreeding depression and male fitness in black grouse

The male lifetime lekking performance was studied, and related to inbreeding-outbreeding in a wild population of black grouse (Tetrao tetrix) in central Finland between 1989 and 1995. Inbreeding was measured as the mean heterozygosity and mean d(2) of 15 microsatellite loci. We found a significantly positive relationship between mean d(2) and lifetime copulation success (LCS), while the relationship between heterozygosity and LCS was close to significant. We also found that males that never obtained a lek territory had significantly lower mean heterozygosity than males that were observed on a territory at least during one mating season in their life. Furthermore, among males that were successful in obtaining a lek territory, LCS and mean d(2) were highest for those males that held central territories. We suggest that inbred males have a disadvantage (or outbred males have an advantage) in the competition for territories that may explain the relationships with LCS and inbreeding. Furthermore, the fact that mean d(2) was positively correlated with LCS whereas heterozygosity was not when we restricted the analysis to territorial males, suggests that mean d(2) provides more information about levels of inbreeding-outbreeding than heterozygosity alone, and potentially highlights the effects of heterosis. To our knowledge, this is the first time that measures of inbreeding and lifetime fitness have been linked in a non-isolated population. This is important in establishing that the relationships found in previous studies are not artefacts of low gene flow created by limited dispersal but a general feature of wild vertebrate populations.     

Effects of natal male alliances on aggression and power dynamics in rhesus macaques

In the wild, male rhesus macaques disperse at sexual maturity. In captivity, however, males cannot disperse from their natal groups. Thus, the presence of natal males in captive rhesus social groups is unnatural and has the potential to negatively influence group dynamics and stability. A primary difference between natal males and non-natal (immigrant) males is that natal males have the opportunity to form long-term alliances with their maternal kin as well as nonkin. We investigated the factors associated with natal males' kin alliances and the impact of these alliances on measures of natal male behavior, group dynamics, and group stability. We found that natal males more frequently formed alliances with maternal kin when they were from high-ranking matrilines, had more siblings, and were younger. More frequent kin alliances were associated with more frequent use of intense aggression, higher individual rank, and higher degree of integration within the male displacement network. Thus, it seems that natal males use their alliances to be more active and influential in the social group, which may affect group stability. It appears that juvenile natal males from high-ranking matrilines, in particular, have the largest impact on group stability. Younger natal males from high-ranking matrilines formed alliances with kin more frequently and used intense aggression more frequently than older or lower ranking males. Furthermore, groups with a higher proportion of juvenile males from high-ranking matrilines also had higher rates of wounding. We suggest that the presence of natal males in rhesus groups may act in opposition to group stability.     

DDT resistance, epistasis and male fitness in flies

In Drosophila melanogaster, the DDT resistance allele (DDT-R) is beneficial in the presence of DDT. Interestingly, DDT-R also elevates female fitness in the absence of DDT and existed in populations before DDT use. However, DDT-R did not spread regardless of DDT-independent selective advantages in females. We ask whether sexual antagonism could explain why DDT-R did not spread before pesticide use. We tested pre- and post-copulatory male fitness correlates in two genetic backgrounds into which we backcrossed the DDT-R allele. We found costs to DDT-R that depended on the genetic background in which DDT-R was found and documented strong epistasis between genetic background and DDT-R that influenced male size. Although it remains unclear whether DDT-R is generally sexually antagonistic, or whether the fitness costs noted would be sufficient to retard the spread of DDT-R in the absence of DDT, general fitness advantages to DDT-R in the absence of DDT may be unlikely.     

Blood parasites and male fitness in the pied flycatcher

In vertebrates the effect of parasites on host ecology has almost been ignored. Recently the view that well-adapted parasites do not harm their hosts has been challenged and there is growing evidence that parasites do have a present-day effect on a great variety of host fitness components. The pied flycatcher is a small migratory passcrine bird. Any decrease in condition caused by disease should affect its ability to cope with physical demands of migration. Here we examine whether blood parasites have any effect on male arrival time. Males infected with Trypanosoma arrived on average 2 days later than males with no Trypanosoma infection. Infected males also had shorted tails and tended to have shorter wings. By contrast, there was no difference in male arrival time between males infected with Haemoproteus and healthy males. It seems that Trypanosoma infection lowered male condition and consequently the ability to moult and migrate. The difference in length of feathers may have generated the difference in arrival times. Early arrival is highly important for males, since only the first males become polygynous and breeding prospects deteriorate rapidly with any delay in egg laying. Estimated reduction in breeding success for infected males was about 20%.     

Exposure to light enhances pre-adult fitness in two dark-dwelling sympatric species of ants

Background  

In insects, circadian clocks play a key role in enhancing fitness by regulating life history traits such as developmental time and adult lifespan. These clocks use environmental light/dark (LD) cycles to fine-tune a wide range of behavioral and physiological processes. To study the effect of environmental LD conditions on pre-adult fitness components, we used two dark-dwelling sympatric species of ants (the night active Camponotus compressus and the day active Camponotus paria), which normally develop underground and have fairly long pre-adult developmental time.     

Body size and fitness relation in male and female Diaeretiella rapae

A strong relationship exists between body size and fitness in parasitoids. However, it is unclear whether the relationship is symmetric or asymmetric in males and females. The present study investigated the body size and fitness relationship in Diaeretiella rapae emerged from small and large nymphs of cabbage aphid Brevicoryne brassicae. A positive relationship existed between the size of the aphid host and growth of parasitoid larva developing in it. The fitness gain in males and females was not proportionate to their body size gain. Females mated with larger males produced 10?% more female offspring than females mated with smaller males. However, females that developed in large hosts produced 62?% more offspring (total male and female) than the females emerged from smaller hosts. The findings suggest that the number of offspring and the progeny sex ratio were affected by the body size of both male and female D. rapae.     

Reproductive costs to male and female worm pipefish

Prior to reproductive maturity male and female worm pipefish Nerophis lumbriciformis are not significantly different in standard length ( L _S), eviscerated mass or condition indices. Subsequently, however, mature females achieve significantly ( P  < 0·001) greater values of L _S and mass. For egg-bearing males, there was no marked difference in the mass of embryos with increasing development ( P  > 0·1); similarly there was no significant divergence in condition indices calculated for males carrying embryos of increasing development. Post-brooding males, however, had significantly lower values for the hepato-somatic index than either egg-bearing or non-mated male worm pipefish ( P  < 0·001). This study suggests that male worm pipefish invest a significant proportion of their energy budget into the development and maintenance of the brooding patch, to the detriment of increased length or mass.