It has been proposed that inbreeding contributes to the decline and eventual extinction of small and isolated populations,. There is ample evidence of fitness reduction due to inbreeding (inbreeding ...depression) in captivity and from a few experimental, and observational field studies,, but no field studies on natural populations have been conducted to test the proposed effect on extinction. It has been argued that in natural populations the impact of inbreeding depression on population survival will be insignificant in comparison to that of demographic and environmental stochasticity,. We have now studied the effect of inbreeding on local extinction in a large metapopulation of the Glanville fritillary butterfly (Melitaea cinxia). We found that extinction risk increased significantly with decreasing heterozygosity, an indication of inbreeding, even after accounting for the effects of the relevant ecological factors. Larval survival, adult longevity and egg-hatching rate were found to be adversely affected by inbreeding and appear to be the fitness components underlying the relationship between inbreeding and extinction. To our knowledge, this is the first demonstration of an effect of inbreeding on the extinction of natural populations. Our results are particularly relevant to the increasing number of species with small local populations due to habitat loss and fragmentation.
The purpose of a study was to experimentally test the hypothesis that inbreeding depression increases the risk of extinction of small butterfly populations. Melitaea cinxia populations were started ...with offspring of full-sib matings or with offspring of outbred matings.
The behaviour of reproductive ant females and males was examined in mating experiments in laboratory conditions. The aims were to identify mechanisms affecting sexual selection in ants in general, ...and to explore more specific issues applicable to the reproductive strategies present in ants like F. aquilonia characterized by a multinest/multiqueen (polydomous/polygynous) organisation of colonies. The mating process was described from video recordings. Multiple mating by both sexes was demonstrated and the observed mating frequency was in good agreement with results for the effective number of matings based on allozyme mother—offspring analyses. For females and males random mate choice was indicated. In choice experiments neither differences between the frequencies of intra- and interpopulation copulations occured, nor did the mating status of males and females affect the pattern of random mating. However, the number of preceding copulations affected the duration of different parts of the mating process in both males and females. Thus, female mating resistance tends to increase after several matings, whereas in males the duration of genital contact increases with the number of previous copulations. Also, male mating experience reduces the time used to get into genital contact, except when multiple copulations occur within a short time. The operational sex ratios in the experimental chamber did not affect the pattern of random mate choice. Spermathecal sperm counts correlated with the number of female matings and were comparable with both the estimated number of sperm for virgin males, and the spermathecal counts for old and young queens collected in the field. The findings are discussed in relation to general patterns of sexual selection in ants. Selection acting on male mating behaviour might drive both female and male multiple mating in F. aquilonia.
Genetic organization of colonies and populations of the ant Formica aquilonia were studied at the edge of the urban area of the city of Helsinki within an area of about 400 km2. Over six thousand old ...queens and workers were sampled from a total of 288 nest mounds from 14 populations (patches of forest) for an allozyme study, and workers from 13—15 nests in each of three populations were also characterized by microsatellite genotyping. Genetic relatedness among nest mates within populations was close to zero for both queens (estimates ranging from 0.02 to 0.13) and workers (from 0.01 to 0.22), with some of the estimates being significantly greater than zero. These results supported the view of a high level of polygyny within the nests. The populations showed significant genetic differences both at the allozyme loci (overall FST = 0.17) and at the microsatellites (FST = 0.24). The estimates of FST between pairs of populations varied from 0.01 to 0.61, the largest values being associated to reduced genetic variation and an apparent bottleneck within one population. The results showed that the local populations of this highly polygynous (multiple queens in a nest) and polydomous (multiple nests in a colony) ant can be differentiated genetically within potential dispersal distances, suggesting restricted dispersal and possible bottlenecks when colonizing new patches of forest.
The effects of inbreeding on fitness and themaintenance of genetic load in metapopulationsof the endangered Glanville fritillarybutterfly (Melitaea cinxia) were examinedin four laboratory ...experiments. In FinlandM. cinxia occurs as a large metapopulationconsisting of small local populations with fastturnover, whereas in southern France thespecies has a more continuous populationstructure. In the experiments, we compared theperformance of crosses between full sibs,crosses between members of different familieswithin populations, and crosses betweenindividuals from different populations. Theseexperiments were replicated using insects fromtwo different regions, Finland and southernFrance, between which the frequency of naturalinbreeding should differ substantially becauseof differing population structure. In Finnishbutterflies, the rate of successful mating waslower among insects derived from small thanfrom large natural populations, probablyreflecting the effect of past inbreedinghistory. Mating between full sibs lowered egghatching rate in all experiments. Thisreduction of egg hatching rate was more severeamong French butterflies with a more continuouspopulation structure than among Finnishbutterflies with small naturally fragmentedpopulations and with a history of repeatedrounds of inbreeding in the past. This resultsuggests that recurrent inbreeding has led topartial purging of deleterious recessives fromthe Finnish metapopulation. Nonetheless,substantial genetic load still remains in thismetapopulation, and we discuss possible reasonswhy this should be the case.PUBLICATION ABSTRACT
This work examines behavioural relationships between young females (potential queens) and workers, in a multi-nest population (supercolony), of Formica lugubris. Each nest contains hundreds of ...functional queens but the colony is initiated by a single foundress (secondary polygyny). Thus, recruitment of new queens into the nests is part of the population dynamics. Substantial variation in worker response towards introduced female sexuals, ranging from execution to complete acceptance, is demonstrated. The mating status of the introduced females has a clear effect on the worker response: virgin females are accepted with about twice the probability of inseminated females. When native alates are present in a nest, all introduced females are accepted with higher probability than when the native alates are absent, later in the season. No effect of distance (between donor and recipient nests) on the worker reaction was found, within the supercolony borders. Proximate mechanisms and selective forces regulating the recruitment process are discussed in light of these findings.
The inner nest temperature in field colonies of ants of the F. rufa group was studied with thermograph recordings and spot sampling. The observations indicate that in colonies with a worker ...complement exceeding 1 million, nest-warming after winter could start as an autocatalytic process and hence may not require triggering by sunning behaviour. In the colony studied with the thermograph the intranest temperature remained at a stable level, near 30°C in late spring and summer, even when the outside temperature temporarily dropped below freezing point. A slight "overshoot" or increase in inner nest temperature, was evident, however, when the outside temperature dropped below the threshold for ant activity in spring. It was found that nests later producing sexuals maintain a significantly higher inner temperature in spring than nests later producing only worker broods. The nest-warming effect of insolation is considered more important in small or weak colonies, whereas endogenous nest heating, based on the metabolism of the ants and their clustering behaviour, is more compatible with the observations in the case of vigorous colonies. The recordings suggest that a capacity for social thermoregulation is a cause of thermal stability in red wood ant nests.
Laboratory experiments confirm that protein-starved red wood ants of the Formica rufa group and Formica truncorum Fabr. react to the presence of protein baits in the foraging area with alerting and ...orienting signals resulting in directional recruitment. Evidence is presented that the cause of directional recruitment in F. rufa group ants is a scent trail laid from the bait toward the nest, while "centripetal" recruitment, due to orienting signals provided by scouts returning to the bait from the nest, is of negligible importance. An interesting complication was detected in F. truncorum, which showed adequate communication of direction to a food source in the light, but not in the dark. Alternative explanations for the latter phenomenon are discussed. The laboratory results are related to field observations of red wood ant colonies, which indicate a rather limited use of directional recruitment, because of the stable distribution of resources. It is pointed out, however, that temporary shortages of resources, especially in spring, may have favoured evolution of mechanisms for directional recruitment.
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