Evolutionary consequences of non-random mating: do large males increase offspring fitness in the anuran Bufo bufo?

The purpose of my study was to determine whether male body size, a trait known to be important to mating success, covaries with offspring performance. I tested the effects of male body size on the performance of Bufo bufo tadpoles reared at two food levels by mating large, small, and naturally-mated males to the same females. Survival of tadpoles in the high-food environment was affected by male size class, but in the opposite way to that expected. Tadpoles sired by large males had the lowest survival, and those sired by small males the highest. Neither body size at metamorphosis nor larval period were affected by male size class alone, but male size interacted with the female contribution: tadpoles sired by large males had short larval periods and large size at metamorphosis with some females,but long larval periods and small body sizes with others. Food level had a significant effect on both size at metamorphosis and larval period, and interacted with female contribution, but not male size class. This indicated that female contribution to tadpoles was dependent on food level, but that the effects of male size were not differentially expressed by tadpoles at the two food levels. My results indicate that traits with a direct effect on offspring fitness are not enhanced by large male body size, yet some males and females produced offspring with significantly better performance. I suggest that evolutionary change in this mating system is unlikely to occur through the non-random mating of males based on body size alone.     

Resource allocation,brood production and cannibalism during colony founding in the fire ant,Solenopsis invicta

Summary The colony founding characteristics of newly mated fire ant queens from monogyne colonies were studied in the field and in the laboratory under haplo- and pleometrotic conditions. Initial queen weight (live) was not correlated with subsequent progeny production. During founding, queens lost a mean of 54% of their lean weight, 73% of their fat weight and 67% of their energy content. The percentage of fat decreased from 44% to 33%. Queens lost weight or energy in relation to the amount of progeny they produced (Figs. 1, 2). The efficiency of the conversion of queen to progeny increased as more progeny were produced, leading to a decline in the unit cost of progeny (Fig. 3). The more minims a queen produced, the lower the mean weight of these minims and the faster they developed (Fig. 4). In a field experiment on pleometrotic founding, total brood increased with queen number, peaked between four and seven queens and declined with 10 queens (Fig. 5). Brood developed faster at the sunny, warmer site, but total production and queen survival was higher at the shady site. As queen density increased, production per queen decreased as a negative exponential in which the exponent estimated sensitivity of brood production to queen-crowding and the constant estimated the production by solo queens (Fig. 9). These effects of queen number were confirmed in laboratory experiments. The decrease of production per queen was small and not always detectable during the egg-laying phase, but brood attrition was always strong during the larval period and increased with queen number (Figs. 8, 10). While airborne factors may have contributed to this inhibition, most of the brood reduction was due to other causes, probably cannibalism. For a given number of minims, increased queen number increased the mean weight of these minims, an effect that resulted both from a lower minim production per queen and from cannibalism of dead queens by survivors (Fig. 11). Cannibal queens lost much less weight to produce a given number of minims than unfed control queens, and these minims were heavier (Fig. 12).     

Bimodality of the combined removal and signs-of-activities estimator for sampling closed animal populations

The possibility of a bimodal log-likelihood function arises with certain data when the combined removal and signs-of-activities estimator is used. Bimodal log-likelihoods may, in turn, yield disjoint confidence intervals for certain confidence levels. The hypothesis that bimodality is caused by the violation of the equal catchability assumption of the removal model, leading to the combination of contradictory data/models in the combined estimator is set forth. Simulations exploring the effect of the violation of removal model assumptions on estimation and inference showed that the assumption of unequal capture probability influenced the frequency of bimodal likelihoods; similarly, extreme parameter values for probability of capture influenced the number of excessively large confidence intervals produced. A sex-specific combined estimator is developed as a remedial model tailored to the problem. The simulations suggest that both the signs-of-activities estimator and the sex-specific estimator perform equally well over the range of simulations presented, though the signs-of-activities estimator is easier to implement.     

Mate choice tactics and swarm size: a model and a test in a dance fly

In the dance flyEmpis borealis (L.) (Diptera: Empididae) females gather to swarm and males visit swarms for mating. A model was constructed, based on previously published data, simulating how males may choose among females of different sizes in swarms of different sizes. The focal question was, what influences the number of individuals in the swarm in this and possibly other swarming insects? The relationships between original swarm size and both the number of males arriving per minute and the proportion of males mating are both logarithmic. The model predicted that if these relationships were linear, or if males were able to judge absolute female size, the mean swarm size should increase and be at least four times as large as those found in the field. The only type of male mate choice strategy that gave rise to very large swarms (>25) was size-related choice (if males are able to assess the size of a female in relation to the entire population and not merely to the swarm). Furthermore, no swarming behaviour would occur if males mate independently of swarm size. Thus, the numbers of females attending a given swarm site are influenced by male arrival pattern, male preference for larger swarms, the inability of males to judge the absolute body size of females, and female polyandry. Males searching for mates seem to prefer larger swarms than females searching for a swarm to join, but the mean swarm size is primarily set by the swarm size preference of females. Optimal swarm size predicted from the model was 4.68±0.53 females. In order to test model predictions, 69 natural swarm sites were studied during one season. The mean swarm size was 4.85±4.54 females (median 4.03), and about 90% of swarms consisted of 11 females or fewer. Predicted and observed swarm size did not differ significantly.     

Estimating Population Size of Elusive Animals with DNA from Hunter-Collected Feces: Four Methods for Brown Bears

Abstract:  Noninvasive genetic methods can be used to estimate animal abundances and offer several advantages over conventional methods. Few attempts have been made, however, to evaluate the accuracy and precision of the estimates. We compared four methods of estimating population size based on fecal sampling. Two methods used rarefaction indices and two were based on capture-mark-recapture (CMR) estimators, one combining genetic and field data. Volunteer hunters and others collected 1904 fecal samples over 2 consecutive years in a large area containing a well-studied population of brown bears ( Ursus arctos ). On our 49,000-km² study area in south-central Sweden, population size estimates ranged from 378 to 572 bears in 2001 and 273 to 433 bears in 2002, depending on the method of estimation used. The estimates from the best model in the program MARK appeared to be the most accurate, based on the minimum population size estimate from radio-marked bears in a subsection of our sampling area. In addition, MARK models included heterogeneity and temporal variation in detection probabilities, which appeared to be present in our samples. All methods, though, incorrectly suggested a biased sex ratio, probably because of sex differences in detection probabilities and low overall detection probabilities. The population size of elusive animals can be estimated reliably over large areas with noninvasive genetic methods, but we stress the importance of an adequate and well-distributed sampling effort. In cases of biased sampling, calibration with independent estimates may be necessary. We recommend that this noninvasive genetic approach, using the MARK models, be used in the future in areas where sufficient numbers of volunteers can be mobilized.     

Harem choice and breeding experience of female southern elephant seals influence offspring survival

Female mammals can increase their lifetime fitness through modification of investment potential and by providing better rearing environments with improved breeding experience. We examined the relationships between reproductive fitness and the behavioural decisions that female southern elephant seals (Mirounga leonina) made during the breeding season. We examined whether mother age and breeding experience influenced reproductive success (measured as 1st-year survival probability), and whether there was a change in the choice of harem size with increasing age. Pups produced by young mothers had lower 1st-year survival probability than pups produced by older mothers. A significant increase in mean female mass with age required an analysis of both these effects on offspring survival. There was a significant positive effect of both female age and mass, and the interaction between the two, on 1st-year pup survival. The proportion of young mothers (<5 years old) decreased and the proportion of older mothers (>6 years old) increased with increasing harem size (harems surveyed from 1997 to 2001). Females chose larger harems in which to breed as they aged. Females demonstrated fidelity to breeding areas among successive breeding seasons, with older females displaying greater breeding-site fidelity than younger females. The mean number of previous breeding attempts per female within a harem (breeding experience) increased significantly with increasing harem size. Breeding females returned to breed later in the breeding season as they aged—we hypothesize that young, subordinate females gain a priority advantage by returning earlier. These results lend support to the hypothesis that there are fitness advantages, in terms of offspring survival, that are conferred to females that breed in successively larger harems with age. Potential mechanisms that select for females to improve their breeding conditions include improved mate selection and the avoidance of conspecific harassment in harems.Communicated by F. Trillmich     

Brood size manipulation affects frequency of second clutches in the blue tit

The reproductive trade-off hypothesis predicts that the investment made in current reproduction determines the breeders’ future fitness as a consequence of intra-or inter-generational reproductive costs. Long-lived species are expected to favour their own reproductive value at the expense of their offspring, hence incurring in inter-generational costs, whereas short-lived species are expected to invest in the current breeding attempt even at the expense of their own survival, thus incurring in intra-generational costs. We tested whether intensity of current reproductive effort has intra-or inter-generational costs in a short-lived bird, the blue tit Parus caeruleus, with a brood size manipulation experiment. We expected more intra-generational (parental reproduction and/or survival) than inter-generational (offspring quality and survival) reproductive costs. We found that parental effort, measured as the hourly rate of parental visits to nests, increased gradually with experimental manipulation. Brood size manipulation resulted in a gradual increase in the number of fledglings per nest from reduced to increased treatments. We found an effect of the manipulation on the probability of making a second clutch, with adults rearing enlarged broods being less likely to undertake such a second reproduction during the season compared to those rearing control or decreased broods. We found no evidence of other reproductive costs; neither as adult weight after manipulation, apparent parental local survival, apparent offspring local survival or local recruitment. Although the results seem to support the a priori expectations, alternative explanations are discussed.Communicated by M. Soler     

Female mate choice in the non-territorial lizard Ameiva plei (Teiidae)

Mate choice by females has been documented in a variety of taxa. Female mate choice in species lacking male resource control or paternal care might occur if preferred males provide protection from harassment. Female mate choice was investigated in a natural population of the non-territorial lizard Ameiva plei (Teiidae). Consort pairs were allowed to form naturally. Consort males were significantly larger than non-consort males. After removal of consort males, the “abandoned” female's reaction to the first male who approached her was recorded. Females rejected all small males. Female preference for large males was significantly higher than preference for small males. Large males may be better equipped to guard the females from harassment and behavior of large males is less harassing than behavior of small males, thereby affording the female increased foraging time. Received: 21 June 1996 / Accepted after revision: 28 December 1996     

Long-Term Landscape Change and Bird Abundance in Amazonian Rainforest Fragments

Abstract:  The rainforests of the Amazon basin are being cut by humans at a rate >20,000 km²/year, leading to smaller and more isolated patches of forest, with remaining fragments often in the range of 1–100 ha. We analyzed samples of understory birds collected over 20 years from a standardized mist-netting program in 1– to 100-ha rainforest fragments in a dynamic Amazonian landscape near Manaus, Brazil. Across bird guilds, the condition of second growth immediately surrounding fragments was often as important as fragment size or local forest cover in explaining variation in abundance. Some fragments surrounded by 100 m of open pasture showed reductions in insectivorous bird abundance of over 95%, even in landscapes dominated by continuous forest and old second growth. These extreme reductions may be typical throughout Amazonia in small (≤10 ha), isolated fragments of rainforest. Abundance for some guilds returned to preisolation levels in 10- and 100-ha fragments connected to continuous forest by 20-year-old second growth. Our results show that the consequences of Amazonian forest loss cannot be accurately described without explicit consideration of vegetation dynamics in matrix habitat. Any dichotomous classification of the landscape into "forest" and "nonforest" misses essential information about the matrix.