GENETIC VARIATION AND JUVENILE SURVIVAL IN RED DEER

The survival of red deer (Cervus elaphus L.) calves to two years of age was examined in relation to electrophoretic variation in a population on the Scottish island of Rhum. Survival was analyzed using logistic analysis in which the “phenotypic” factors birth weight, birth date, subdivision of the study area, cohort, and sex, which affect the probability of a calf's survival, were taken into account. All three polymorphic loci examined, Mpi, Idh-2, and Trf (each with two detected alleles) are significantly associated with juvenile survival. At Mpi, there is selection against one allele, f (or an allele at a linked locus), and there are indications that this effect is stronger in females than males. For Idh-2, overall, the heterozygote class survives better than the two homozygotes, which survive equally well. However, again there is a difference between the sexes; female heterozygotes survive much better than homozygotes, whereas male homozygotes survive better than heterozygotes, and the difference in survival is smaller. Furthermore, there is an interaction involving Mpi, Idh-2, and survival in which Mpi^f carriers that are also Idh-2 homozygotes survive very badly compared with other Mpi-Idh-2 combinations, which all survive equally well. For Trf, the heterozygote class survives best, and there is also a difference in survival between the two homozygote classes. Genotype frequencies in the adult population are consistent with the results for calf survival, in that the Mpi^f frequency is lower in succeeding cohorts of surviving adults, whereas no significant gene frequency change is apparent for Idh-2 or Trf.     

Esterase-2 in Ephestia kühniella. I. Genetics and characterization

At the gene locus for esterase-2 (E.C. 3.1.1.1) of the meal moth Ephestia kühniella, three autosomally inherited and codominantly expressed alleles exist. In the homozygous condition, the alleles 2 ^s , 2 ^m , and 2 ^f determine the subunits s, m, and f which aggregate to form enzymatically active molecules, probably dimers, found in starch gel as single bands of slow, intermediate, and fast mobility. In the heterozygous state, however, three-banded patterns are found, composed of the two homodimer parental bands and a heterodimer band of intermediate mobility. Inactivation of the bands by treatment with heat and 4 m urea has been followed quantitatively. The ff band is inactivated faster than the mm, ss, and ms bands, all of which are inactivated at the same rate. Hybrid fm and fs bands, however, show intermediate inactivation rates.This work was supported by the Deutsche Forschungsgemeinschaft and submitted with Part II in partial fulfillment of the requirements for the degree of Dr.-habil. at the University of Tübingen.     

INTERTIDAL MICROHABITAT AND SELECTION AT MPI: INTERLOCUS CONTRASTS IN THE NORTHERN ACORN BARNACLE,SEMIBALANUS BALANOIDES

Barnacles were sampled from various microhabitats in the rocky intertidal at multiple sites in two years. At sites in which there were large differences among microhabitats in temperature profiles, Mpi genotype frequencies were consistently and significantly different. Genotype frequencies for another allozyme locus (Gpi) as well as a DNA marker shown to be neutral (the mtDNA control region) were statistically homogeneous among thermal microhabitats at all sites in both years. The data indicate that temperature and/or desiccation mediated selection is operating at Mpi or a linked locus and that Mpi genotypes experience differential mortality in the various habitat types. If the relative fitness of genotypes is dependent on habitat type, the Mpi polymorphism may be actively maintained by a Levene model of balancing selection (Levene 1953). Because barnacle larvae are produced in abundance each year and spend five to eight weeks dispersing in the water column, there is little opportunity for the accumulation of adaptive divergence over the environmental grain size relevant in intertidal habitats. The Mpi polymorphism may be an important component of a suite of traits involved in the adaptation of barnacles to heterogeneous environments. Due to the relatively high concentration of mannose in a variety of algal groups, the metabolism of mannose may substantially affect individual performance and fitness in this and other species that feed on algae and phytoplankton. Because the Mpi locus is one of the most strongly polymorphic in marine organisms, these findings may be relevant for a diversity of other such species.     

Extrinsic and intrinsic factors influence fitness in an avian hybrid zone

The effects of hybridization on evolutionary processes are primarily determined by the differential between hybrid and parental species fitness. Assessing the impacts of hybridization can be challenging, however, as determining the relationship between individual fitness and the extent of introgression in wild populations is difficult. We evaluated the fitness consequences of hybridization for pure and hybrid females in a hybrid zone between two tidal marsh birds, the saltmarsh sparrow (Ammodramus caudacutus), a salt marsh obligate, and Nelson's sparrow (A. nelsoni), which has a broader ecological niche and a much younger evolutionary association with salt marshes. Biotic stressors associated with nesting in tidal environments suggest an important role for differential adaptation in shaping hybrid zone dynamics, with saltmarsh sparrows predicted to be better adapted to nesting in salt marshes. We collected DNA samples from adults (n = 394) and nestlings (n = 431) to determine the extent of introgression using 12 microsatellite loci and tested for the influence of extrinsic (nest placement) and intrinsic (genotype) factors on female reproductive success. We monitored nests (n = 228), collected data on reproductive output, and estimated daily nest survival rates using female genotype and nest characteristics as covariates. To test for reduced survival of hybrid females, we also used capture data to assess the distribution of admixed male and female individuals across age classes. Reproductive success of females varied by genotypic class, but hybrids did not have intermediate success as predicted. Instead, we found that pure Nelson's sparrows had, on average, 33% lower hatching success than any other genotype, whereas F1/F2 hybrids, backcrossed Nelson's sparrows, and backcrossed and pure saltmarsh sparrows all had similar hatching success. We found no effect of genotype or nest placement on daily nest survival probabilities. However, hybrid individuals with a higher proportion of saltmarsh sparrow alleles exhibit nesting behaviours better suited to nesting successfully in tidal marshes. Further, while the proportion of F1/F2 individuals was similar between nestling and adult males, we found that the proportion of F1/F2 individuals was 2.3 times greater in nestling females compared with adult females, indicating reduced survival of F1 females. We conclude that differences in reproductive success among pure and admixed individuals coupled with intrinsic mechanisms (reduced survival in F1 females) shape hybrid zone dynamics in this system.     

Isolation by distance and a chromosomal cline in the Cayapa cytospecies of <Emphasis Type="Italic">Simulium exiguum</Emphasis>, the vector of human onchocerciasis in Ecuador

The population genetic structure of the Cayapa cytospecies of Simulium exiguum, the vector of onchocerciasis, was analysed using allozyme frequency and chromosomal inversion polymorphism data from 6 and 15 populations respectively, collected in Ecuador. Eight allozyme loci were scored. No unique allozyme markers were found enabling us to identify biting adults of the vector from the non-vector Bucay cytotype. Mannose-phosphate isomerase (Mpi) contributed largely to the significant heterogeneity in gene frequency among populations of the Cayapa cytospecies and also to the overall population structuring (F_ST=0.015 ± 0.014) which fitted the isolation by distance model. However, heterozygote deficits were recorded for Mpi in four of the six populations, which could indicate that selection is acting at this locus but this hypothesis will require further convincing evidence. Furthermore the significant population structuring of allozymes was not evident when Mpi was omitted from the analysis. All inversion polymorphisms (IIS-B, IIS-F, IIL-A and IIL-B) were in Hardy-Weinberg equilibrium, showed significant heterogeneity between populations and revealed the occurrence of an altitudinal cline in inversion IIS-B frequency. The inversion polymorphisms revealed a significant degree of population structuring (F_ST=0.083 ± 0.027), which can be explained by the isolation by distance model. A UPGMA cluster analysis revealed the relatively remote, high altitude Rio Mira populations to be the most genetically distinct.     

A FIELD TEST FOR HOST-PLANT DEPENDENT SELECTION ON LARVAE OF THE APPLE MAGGOT FLY,RHAGOLETIS POMONELLA

Host-plant dependent fitness trade-offs refer to traits that enhance the performance of an insect on one plant species to its detriment on others. Such trade-offs are central to models of sympatric speciation via host shifts, but have proven difficult to empirically demonstrate. Here, we test for host-plant dependent selection on larvae of apple (Malus pumila L.)- and hawthorn (Crataegus mollis L. spp.)-infesting races of Rhagoletis pomonella (Walsh). Samples of larvae were reared in the field and under protective conditions in a garage. Our rationale was that the garage should slow rates of fruit rot relative to the field, relaxing selection pressures associated with declining fruit quality. Four findings emerged from the study. (1) Larvae suffered higher mortality in fruits in the field than the garage. (2) The increase in mortality was greater for larvae in haws. (3) Larvae possessing the alleles Me 100, Acon-2 95, and Mpi 37, three allozymes displaying host-related differentiation in R. pomonella that map to linkage group II in the fly, left fruits earlier than other genotypes. (4) Allele frequencies for Me 100, Acon-2 95, and Mpi 37 were significantly higher in both apple and haw larvae surviving the field versus the garage treatment. Our results suggested that field conditions favored larvae that rapidly developed and left rotting fruits. Since these individuals tended to possess the alleles Me 100, Acon-2 95, and Mpi 37, frequencies of these allozymes were higher in the field. Selection on larvae was directional for Me 100, Acon-2 95, and Mpi 37 (or linked genes) in both host races. We previously showed that these same alleles can be disfavored in the pupal stage, especially in the apple race, where they correlate with premature diapause termination. Fitness trade-offs in Rhagoletis may therefore be due as much to differences in the relative strengths of directional selection pressures acting on different life stages as to disruptive selection affecting any one particular stage. The necessity to consider details of the entire life-cycle highlights one of the many challenges posed to documenting fitness trade-offs for phytophagous insects.     

What is driving male mate preference evolution in Jamaican field crickets?

Male mating preferences are often a neglected aspect of studies on sexual selection. Male mating preferences may evolve if they provide males with direct‐fitness benefits such as increased opportunity to fertilize more eggs or indirect‐fitness benefits such as enhanced offspring survival. We tested these ideas using Jamaican field crickets, Gryllus assimilis, previously shown to exhibit male mating preferences. We randomly mated males to either their preferred or non‐preferred potential mates and then asked whether mating treatment influenced egg oviposition or offspring viability. Preferred females were not significantly more fecund and did not produce more viable eggs or offspring than non‐preferred females. Male mate preferences were therefore inconsistent with both the direct‐ and indirect‐fitness benefits hypotheses under the conditions of our experiment. Our null results leave us with an open question about what is driving the evolution of mating preferences in male crickets. Future research should explore the whether the offspring of preferred females are more attractive, have stronger immune systems, and/or experience higher adult longevity.     

Inbreeding coefficient and heterozygosity–fitness correlations in unhatched and hatched song sparrow nestmates

Heterozygosity–fitness correlations use molecular measures of heterozygosity as proxy estimates of individual inbreeding coefficients (f) to examine relationships between inbreeding and fitness traits. Heterozygosity–fitness correlations partly depend on the assumption that individual heterozygosity and f are strongly and negatively correlated. Although theory predicts that this relationship will be strongest when mean f and variance in f are high, few studies of heterozygosity–fitness correlations include estimates of f based on pedigrees, which allow for more thorough examinations of the relationship between f, heterozygosity and fitness in nature. We examined relationships between pedigree‐based estimates of f, multilocus heterozygosity (MLH) and the probability of survival to hatch in song sparrow nestmates. f and MLH were weakly, but significantly negatively correlated. Inbreeding coefficient predicted the probability of survival to hatch. In contrast, MLH did not predict the probability of survival to hatch nor did it account for residual variation in survival to hatch after statistically controlling for the effects of f. These results are consistent with the expectation that heterozygosity–f correlations will be weak when mean and variance in f are low. Our results also provide empirical support for recent simulation studies, which show that variation in MLH among siblings with equal f can be large and may obscure MLH–fitness relationships.     

BALANCING SELECTION IN A DESERT STREAM-DWELLING FISH,POECILIOPSIS MONACHA

The desert stream-dwelling fish Poeciliopsis monacha is exposed to extreme seasonal and spatial variation in physical stresses. We examined four diallelic gene loci (Ldh-1, Idh-2, Pgd, and Ck-A) in P. monacha and tested whether genotypes were associated with differential survival of individuals exposed to acute stress. For each locus, the common allele was associated with higher survival during heat and hypoxic stress, whereas the alternate allele was associated with higher survival during cold stress. In most cases, survival of heterozygotes was intermediate and they exhibited less variance in survival than corresponding homozygotes. Identification of substantial linkage disequilibrium in these fish confounds our ability to discern whether the allozymes are the direct targets of selection, or if they just mark chromosomal regions that contain the true modifiers of survival. Nevertheless, the present results clearly identified balancing processes that can serve to stabilize genetic polymorphism in this species.     

MICROSATELLITE LOCI REVEAL SEX-DEPENDENT RESPONSES TO INBREEDING AND OUTBREEDING IN RED DEER CALVES

Mean d² is a recently devised microsatellite-based measure that is hypothesised to allow the detection of inbreeding depression and heterosis in free-living populations. Two studies that have investigated the measure have both demonstrated an association between mean d² and traits related to fitness. Here we present an association between mean d¹ and an important component of fitness, first-year overwinter survival, in a population of red deer on the Isle of Rum, Scotland. The association between survival and mean d² differed between males and females. As predicted, outbred female calves (high mean d²) survived better than those that were inbred (low mean d²). However, the association was in the opposite direction in male calves. We suggest that this difference is due to different early growth strategies between the sexes. The association between mean d² and survival was not significantly influenced by any single locus. Decomposition of mean d² into a recent inbreeding component and an outbreeding component showed that it was the degree of outbreeding that influenced survival in males and both the degree of outbreeding and recent inbreeding that influenced survival in females. Our analyses suggest that mean d² is an easy-to-calculate measure of inbreeding and degree of outbreeding that can reveal interesting interactions between genetics and ecology.     

Female cuticular hydrocarbons can signal indirect fecundity benefits in an insect

Male choosiness of prospective female mating partners provides an increasingly recognized pathway through which males can increase their fitness. For example, males may increase their number of offspring by targeting more fecund females as mating partners. If fecundity is heritable, males that mate with more fecund females can also receive the indirect benefit of more fecund daughters. In species where female fecundity is not directly assessable, female ornaments may act as signals of fecundity. However, whether female ornaments reliably signal the indirect benefit of more fecund daughters is not well understood. We investigated this question using the field cricket, Teleogryllus oceanicus. Previous work had identified the cuticular hydrocarbon (CHC) profile as a female sexual display trait in T. oceanicus. To examine whether CHCs can provide a reliable signal of fecundity, we tested whether individual CHC compounds and the first principal axis of CHC variation (PC1) are genetically correlated with ovary mass, a reliable proxy for fecundity in this species. We found significant genetic correlations between ovary mass and three individual CHC compounds, as well as PC1. This result indicates that by targeting females as mating partners based on their CHC profile, males can sire more fecund daughters.     

INBREEDING DEPRESSION IN A SELF-COMPATIBLE,ANDRODIOECIOUS CRUSTACEAN,EULIMNADIA TEXANA

The observation that offspring produced by the mating of close relatives are often less fit than those produced by matings between unrelated individuals (i.e., inbreeding depression) has commonly been explained in terms of the increased probability of expressing deleterious recessive alleles among inbred offspring (the partial dominance model). This model predicts that inbreeding depression should be limited in regularly inbreeding populations because the deleterious alleles that cause inbreeding depression (i.e., the genetic load) should be purged by regularly exposing these alleles to natural selection. We indirectly test the partial dominance model using four highly inbred populations of an androdioecious crustacean, the clam shrimp Eulimnadia texana. These shrimp are comprised of males and hermaphrodites, the latter capable of either self-fertilizing or mating with a male (i.e., outcrossing between hermaphrodites is impossible). Hermaphrodites are further subdivided into monogenics (produced via self-fertilization) and amphigenics (produced via self-fertilization or outcrossing). Electrophoretic evidence suggests significant differences in heterozygosity among populations, but that selfing rates were not statistically different (average s = 0.67). Additional electrophoretic analyses reveal that three previously described sex-linked loci (Fum, Idh-1, and Idh-2) are all tightly linked to each other, with crossing over on the order of 1% per generation. Although selfing rates are clearly high, we present evidence that early inbreeding depression (hatching rates, juvenile survival, and age at sexual maturity) exists in all four populations. For all of these factors, inbreeding depression was inferred by the positive correlation of multilocus heterozygosity and fitness. Cumulative inbreeding depression (8) is between 0.41 and 0.47 across all populations, which appears to be too low to limit the effects of purging via identity disequilibrium. Instead, we suggest that the maintenance of inbreeding depression in these populations is due to the observed linkage group, which we suggest contains a large number of genes including many related to fitness. Segregation of such a large linkage group would explain our observations of the predominance of amphigenic hermaphrodites in our field samples and of survival differences between monogenics and amphigenics within selfed clutches. We propose that a modified form of the overdominance model for inbreeding depression operating at the level of linkage groups maintains the observed levels of inbreeding depression in these populations even in the face of high rates of selfing.     

Interspecific hybridization and genetic variability of Phlebotomus sandflies

The first successful hybridization is reported between Phlebotomus papatasi and P. duboscqi, two important Old World sandfly vectors of leishmaniasis and other diseases. Laboratory strains of P. papatasi and P. duboscqi were separable by six diagnostic enzyme loci: Est-3, Idh-1, Mdh-2, Mpi, Tre-1 and Tre-3. Hybrids between the two species were verified by the recovery of heterozygous isozyme patterns for the diagnostic loci. No F2 or backcross progeny were obtained. P. papatasi was separated from P. bergeroti by three diagnostic enzyme loci: Est-3, Mpi and Pgd. The isozyme patterns of P. bergeroti contain elements of both P. duboscqi and P. papatasi, although seven diagnostic loci (Est-3, Idh-1, Me, Mpi, Pgd, Tre-1 and Tre-3) separated P. bergeroti from P. duboscqi. Genetic variability profiles of the three species were established for 20 enzyme loci. Three geographically distant strains of P. papatasi from Calcutta, Maharashtra and Israel had isozyme genetic distances of < 0.05. The recently established Calcutta strain showed an unexpectedly low genetic variability with only one (Idh-2) of 20 loci being polymorphic (average heterozygosity of 1.9%) in contrast to 5-8 polymorphic loci (10-12% heterozygosity) in the Maharashtra and Israel strains. Mass and single pair crosses between the three P. papatasi strains were fertile with normal progeny numbers. Thus we found no signs of speciation in P. papatasi.     

LIFETIME ESTIMATES OF BIPARENTAL INBREEDING DEPRESSION IN THE SELF-INCOMPATIBLE ANNUAL PLANT RAPHANUS SATIVUS

Studies of inbreeding depression in plant populations have focused primarily on comparisons of selfing versus outcrossing in self-compatible species. Here we examine the effect of five naturally occurring levels of inbreeding (f ranging from 0 to 0.25 by pedigree) on components of lifetime fitness in a field population of the self-incompatible annual, Raphanus sativus. Pre- and postgermination survival and reproductive success were examined for offspring resulting from compatible cross-pollinations. Multiple linear regression of inbreeding level on rates of fruit and seed abortion as well as seed weight and total seed weight per fruit were not significant. Inbreeding level was not found to affect seed germination, offspring survival in the field, date of first flowering, or plant biomass (dry weight minus fruit). The effect of inbreeding on seedling viability in the greenhouse and viability to flowering was significant but small and inconsistently correlated with inbreeding level. Maternal fecundity, however, a measure of seed yield, was reduced almost 60% in offspring from full-sib crosses (f = 0.25) relative to offspring resulting from experimental outcross pollinations (f = 0). Water availability, a form of physiological stress, affected plant biomass but did not affect maternal fecundity, nor did it interact with inbreeding level to influence these characters. The delayed expression of strong inbreeding depression suggests that highly deleterious recessive alleles were not a primary cause of fitness loss with inbreeding. Highly deleterious recessives may have been purged by bottlenecks in population size associated with the introduction of Raphanus and its recent range expansions. In general, reductions in total relative fitness of greater than 50% associated with full-sib crosses should be sufficient to prohibit the evolution of self-compatibility via transmission advantage in Raphanus.     

Esterase-2 in Ephestia kühniella. II. Tissue-specific patterns

Esterase-2 polymorphism has been investigated quantitatively. Staining intensities of the homodimer bands mm, ff, and ss are not equally expressed but found in relative activities of 1:0.5:0.7 in fat bodies and 1:1:3 in testes and gut walls. Relative intensities of the parental bands are binomially distributed in the three-banded patterns of heterozygotes in an exactly tissue-specific manner. Organ-specific proportions of relative activity remain constant throughout postembryonic development. Among reasons which may influence genesis of allele- and organ-specific activities of homodimer bands in homozygotes and may lead to asymmetrical distribution of intensities in the patterns of heterozygotes, a hypothesis of differential allelic activity is discussed, according to which the structural alleles 2 ^m , 2 ^f , and 2 ^s are closely linked to the alleles RG ^a , RG ^b , and RG ^c of a controlling gene.This work was supported by the Deutsche Forschungsgemeinschaft and submitted with Part I in partial fulfillment of the requirements for the degree of Dr.-habil. at the University of Tübingen.     

Population Dynamics of Evolutionary Change: Demographic Parameters as Indicators of Fitness

I evaluated demographic parameters as indicators of fitness by calculating the net reproductive rate (R₀), exponential rate of change (r), lifetime reproductive success (LRS), and Malthusian parameter (m) for nine genotypes and four phenotypes (two alleles at each of two independent loci) of an age-structured population. The given starting conditions included age-specific survival rates of males and females and age-specific fecundity of females for each genotype (to simplify the problem I presumed no differences in survivorship or fecundity of genotypes with the same phenotype) and the same age structure for each genotype. The prevailing genotype had the greatestm, but it did not have the greatestr,R₀, or LRS, or even the greatest survivorship of either juveniles or adults, or the greatest fecundity. This result indicates thatmis the only correct measure of fitness (i.e., as a predictor of which genotype should prevail from among a group of genotypes) and that comparisons ofr,R₀, LRS, juvenile or adult survival rates, or fecundity may be misleading indicators of which genotype should prevail (i.e., be most “fit”) over time (i.e., be selected for).     

Flight and Oviposition Behavior of the Adult Maritime Ringlet (Coenonympha nipisiquit McDunnough) Females in Response to Microhabitat

Maritime ringlet butterflies (Coenonympha nipisiquit McDunnough), an endangered species in Canada, inhabit salt marshes, which consist of microhabitat mosaics with varied larval survival rate. These microhabitats may influence the movement and reproductive behaviors of females, which in turn may affect population dynamics. I recorded behaviors and locations of females every minute with a GPS rover and calculated their move lengths and turning angles. Move lengths did not change in response to microhabitats, although turning angles became larger near bodies of water with sparse vegetation. Females spent a longer time in one location and oviposited more often where the principal larval host, Spartina patens (Aiton) Muhl., is abundant, regardless of larval survival rate. Older females tended to initiate flight more readily than younger females and spent more time flying and nectaring. Younger females were more fecund and spent a longer time at one location. Because young females tend to be less mobile and more fecund, the majority of oviposition should take place near eclosion sites. However, some eggs will be laid away from microhabitats favorable to larval survival when older females become mobile and move out of their natal microhabitats. Because it seems to have little potential to colonize new habitat on its own, monitoring population dynamics and habitat quality will be crucial for the persistence and recovery of this rare species.     

The effect of host size on quality attributes of the egg parasitoid,Trichogramma pretiosum

In a study of the quality ofTrichogramma pretiosum Riley (Hymenoptera: Trichogrammidae), we compared female wasps emerging from natural hosts, parasitized in the laboratory or the field with those emerging from factitious hosts used for commercial mass production. Females from the natural hosts were larger, more fecund, and longer lived than those from the factitious hosts. Compared to small females, large female wasps are substantially more fecund when honey (carbohydrate) is available but marginally more fecund when honey is unavailable. The size of a femaleT. pretiosum depends on two factors: the size of the host egg from which it emerges even when the wasp was gregarious, and the number of conspecifics that emerge with it. The similarities in the size distribution of female wasps emerging from natural hosts, in conjunction with the mechanism by whichTrichogramma measure host size and allocate eggs accordingly, suggests the hypothesis that size related components of fitness in femaleT. pretiosum are under strong selection in the field.     

Heterozygosity–fitness correlations in a wild mammal population: accounting for parental and environmental effects

HFCs (heterozygosity–fitness correlations) measure the direct relationship between an individual's genetic diversity and fitness. The effects of parental heterozygosity and the environment on HFCs are currently under‐researched. We investigated these in a high‐density U.K. population of European badgers (Meles meles), using a multimodel capture–mark–recapture framework and 35 microsatellite loci. We detected interannual variation in first‐year, but not adult, survival probability. Adult females had higher annual survival probabilities than adult males. Cubs with more heterozygous fathers had higher first‐year survival, but only in wetter summers; there was no relationship with individual or maternal heterozygosity. Moist soil conditions enhance badger food supply (earthworms), improving survival. In dryer years, higher indiscriminate mortality rates appear to mask differential heterozygosity‐related survival effects. This paternal interaction was significant in the most supported model; however, the model‐averaged estimate had a relative importance of 0.50 and overlapped zero slightly. First‐year survival probabilities were not correlated with the inbreeding coefficient (f); however, small sample sizes limited the power to detect inbreeding depression. Correlations between individual heterozygosity and inbreeding were weak, in line with published meta‐analyses showing that HFCs tend to be weak. We found support for general rather than local heterozygosity effects on first‐year survival probability, and g2 indicated that our markers had power to detect inbreeding. We emphasize the importance of assessing how environmental stressors can influence the magnitude and direction of HFCs and of considering how parental genetic diversity can affect fitness‐related traits, which could play an important role in the evolution of mate choice.     

Effects of inbreeding on fitness‐related traits in a small isolated moose population

Inbreeding can affect fitness‐related traits at different life history stages and may interact with environmental variation to induce even larger effects. We used genetic parentage assignment based on 22 microsatellite loci to determine a 25 year long pedigree for a newly established island population of moose with 20–40 reproducing individuals annually. We used the pedigree to calculate individual inbreeding coefficients and examined for effects of individual inbreeding (f) and heterozygosity on fitness‐related traits. We found negative effects of f on birth date, calf body mass and twinning rate. The relationship between f and calf body mass and twinning rate were found to be separate but weaker after accounting for birth date. We found no support for an inbreeding effect on the age‐specific lifetime reproductive success of females. The influence of f on birth date was related to climatic conditions during the spring prior to birth, indicating that calves with a low f were born earlier after a cold spring than calves with high f. In years with a warm spring, calf f did not affect birth date. The results suggest that severe inbreeding in moose has both indirect effects on fitness through delayed birth and lower juvenile body mass, as well as separate direct effects, as there still was a significant relationship between f and twinning rate after accounting for birth date and body mass as calf. Consequently, severe inbreeding as found in the study population may have consequences for population growth and extinction risk.