Effect of inbreeding and heritability of sperm competition success in the bulb mite Rhizoglyphus robini

Sperm competition is a potent evolutionary force shaping the reproductive biology of most animal species. Here, we estimated the heritability of sperm competition success in the promiscuous bulb mite Rhizoglyphus robini. Sperm competition success was measured with the sterile male technique as the proportion of eggs fertilised by the second of three males mated with a single female. Sperm competition success responded significantly to selection. The heritability estimated from the response to five generations of selection was 0.13. We also estimated the effect of inbreeding on sperm competition success. Males produced by sib-mating (F=0.25) had a significantly lower sperm competition success than outbred males. The estimated coefficient of inbreeding depression was 0.53. Such high inbreeding depression together with moderately low heritability is consistent with the view that sperm competitive ability is under strong directional selection and strongly influences the reproductive success of males.     

Ischemic preconditioning prevents endothelial dysfunction, P-selectin expression, and neutrophil adhesion by preventing endothelin and O2- generation in the post-ischemic guinea-pig heart.

Evidence indicates that ischemia/reperfusion (IR) results in endothelial dysfunction and neutrophil adhesion in the post-ischemic myocardium and that ischemic preconditioning (IPC), superoxide dismutase (SOD), and anti-endothelin-1 (ET-1) interventions prevent these effects. We tested the hypothesis that ET-1-induced superoxide (O(2)(-)) generation mediates endothelial injury and neutrophil accumulation in the IR heart, that IPC protects the endothelium and prevents the adhesion by attenuating post-ischemic ET-1, and thus O(2)(-), generation, and that the mitochondrial ATP-dependent potassium channel (mK(ATP)) triggers the IPC-induced protection. Langendorff-perfused guinea-pig hearts were subjected either to 30 min ischemia/35 min reperfusion (IR) or were preconditioned prior to IR with three cycles of either 5 min ischemia/5 min reperfusion or 5 min infusion/5 min wash-out of mK(ATP) opener diazoxide (0.5 microM). Neutrophils were infused to the hearts at 15-25 min of the reperfusion. Coronary flow responses to acetylcholine (ACh) and nitroprusside (SNP) served as measures of endothelium-dependent and -independent vascular function, respectively. Myocardial outflow of ET-1 and O(2)(-), P-selectin expression, neutrophil adhesion and functional recoveries were followed during reperfusion. IR augmented ET-1 and O(2)(-) outflow, P-selectin expression, and neutrophil adhesion, and impaired ACh response. These effects were attenuated or prevented by IPC and diazoxide, and 5-hydroxydecanoate (a selective mK(ATP) blocker) abolished the effects of IPC and diazoxide. SOD (150 U/ml) and tezosentan (5 nM, a mixed ET-1-receptor antagonist) mimicked the effects of IPC, although they had no effect on the ET-1 generation. The preventive effect of IPC, SOD and tezosentan on P-selectin expression preceded their effect on neutrophil adhesion. These data suggest that in guinea-pig heart: (i) ET-1-induced O(2)(-) generation mediates the post-ischemic endothelial dysfunction, P-selectin expression and neutrophil adhesion; (ii) IPC and diazoxide afford protection by attenuating the ET-1, and thus O(2)(-) generation; (iii) the mK(ATP) opening triggers the IPC protection; (iv) endothelial injury promotes post-ischemic neutrophil adhesion, but not vice versa.     

Strong association between a single gene and fertilization efficiency of males and fecundity of their mates in the bulb mite

Although variation in male fertilization efficiency has been shown to have a genetic basis in several species, the genes responsible for the effect are generally unknown. Here, we show a strong association between the fertilization success of males and their phosphogluconate dehydrogenase (Pgdh) genotype in the bulb mite Rhizoglyphus robini. Males homozygous for the slow (S) allele fathered a significantly greater proportion of offspring when competing with males homozygous for the fast (F) allele. There was no evidence that female fecundity was influenced by their Pgdh genotype. The fecundity of FF females did not differ significantly from the fecundity of SS females but female fecundity was significantly influenced by the genotype of their mate. Females paired with SS males laid significantly fewer eggs than females paired with FF males. Altogether these data show a trade-off, with the male SS genotype associated with their higher fertilization efficiency but at the cost of a negative impact on the fecundity of females mating with them.     

The long-term effect of cadmium exposure through food on the postnatal development of the bank vole (Clethrionomys glareolus Schreber, 1780)

Cadmium is well known for its toxicity to the animal body. However, its effect on pregnancy and the development of young animals is still not well understood. This study examined such effects, using bank voles captured from the wild to make the results closer to those which could be expected in the natural environment. One group of animals was fed 7 microg g(-1) cadmium in the food, a second 35 microg g(-1), and a third no cadmium, as a control. The concentrations of cadmium in the whole bodies of young bank voles were determined on the 3rd, 5th, or 10th day of life. The cadmium level in the bodies of animals exposed to 35 microg g(-1) of cadmium was significantly higher than in those from either the control group or the group receiving 7 microg g(-1) of cadmium, which did not differ from each other. The cadmium level did not change with animal age in any of the study groups. Concentrations of Zn, Cu, and Fe were also determined in the whole body of young animals, as cadmium is known to disturb the metabolism of these essential metals through antagonistic activity. Both Cu and Fe levels were negatively correlated with cadmium concentrations, while a positive correlation was found between zinc and cadmium in the young animal bodies. Also found was higher offspring mortality in the group receiving 35 microg g(-1) of cadmium in food. There was no difference in young animal body weight between the study groups.     

POLYANDRY INCREASES OFFSPRING FECUNDITY IN THE BULB MITE

Abstract The common occurrence of polyandry continues to puzzle evolutionary biologists, as female reproductive success is thought to be limited mostly by her fecundity. Here we test whether females of the bulb mite, a species in which the females are highly promiscuous, benefit from polyandry in terms of increased fitness of their progeny. Females were given opportunity to mate with either one or six males, but the experiment was designed to allow the same number of matings per female in both groups, that is, irrespective of the number of males. We found that daughters of females mated to six males had significantly higher fecundity than daughters of females mated to one male, whereas other fitness components of progeny (male virility and longevity of both sexes) were not affected. These findings appear to support hypotheses proposing that multi-male mating enables females to exercise postcopulatory mate-choice (direct or indirect, via sperm competition) and thus accrue genetic benefits.     

Aggressiveness in Two Male Morphs of the Bulb Mite Rhizoglyphus robini

We studied differences in aggressiveness between two male morphs of the bulb mite Rhizoglyphus robini (Acari: Acaridae). Heteromorphic males have a thickened and sharply terminating third pair of legs, whereas homeomorphic males have unmodified legs. In another genus ( Caloglyphus ) of the family Acaridae, modified legs are used during fights to stab (often mortally) other males, but fights have not so far been observed in the genus Rhizoglyphus .
In this study we showed that in Rhizoglyphus robini males fight in a way similar to that previously described for the genus Caloglyphus. The presence of females increased the duration of aggressive interactions and caused earlier initiation, but fights were also observed in the absence of females. Pairs of heteromorphic males spent more time on aggressive interactions than did mixed pairs of heteromorphs and homeomorphs or pairs of homeomorphic males. Although the proportion of pairs involved in aggressive interactions did not differ between these three morph combinations, clasping of the opponent with legs, which is a typical behaviour of killer Caloglyphus males that precedes stabbing, occurred more often between pairs of heteromorphs than between mixed pairs and pairs of homeomorphs. This is consistent with our other finding that mortality attributable to male aggression was only recorded in pairs of males containing at least one heteromorphic male. We conclude that the modified legs of heteromorphic R. robini males function as a weapon in aggressive interactions between males and that, as previously described for the genus Caloglyphus , male morphs differ in aggressiveness.