Brood sex ratio variation in a cooperatively breeding bird

In cooperatively breeding species, the fitness consequences of producing sons or daughters depend upon the fitness impacts of positive (repayment hypothesis) and negative (local competition hypothesis) social interactions among relatives. In this study, we examine brood sex allocation in relation to the predictions of both the repayment and the local competition hypotheses in the cooperatively breeding long-tailed tit Aegithalos caudatus. At the population level, we found that annual brood sex ratio was negatively related to the number of male survivors across years, as predicted by the local competition hypothesis. At an individual level, in contrast to predictions of the repayment hypothesis, there was no evidence for facultative control of brood sex ratio. However, immigrant females produced a greater proportion of sons than resident females, a result consistent with both hypotheses. We conclude that female long-tailed tits make adaptive decisions about brood sex allocation.     

Male‐specific mortality biases secondary sex ratio in Eurasian tree sparrows Passer montanus

Sex allocation theory predicts that parents bias the offspring sex ratio strategically. In avian species, the offspring sex ratio can be biased at multiple growth stages, although the mechanisms are not well known. It is crucial to reveal a cause and timing of biased offspring sex ratio. We investigated (i) offspring sex ratio at multiple growth stages, from laying to fledging; and (ii) the stage at which offspring sex ratio became biased; and (iii) the cause of biased offspring sex ratio in Eurasian tree sparrows Passer montanus. Sex determination of 218 offspring, including hatchlings and unhatched eggs from 41 clutches, suggested that the offspring sex ratio was not biased at the egg‐laying stage but was significantly female‐biased after the laying stage due to higher mortality of male embryos. Half of the unhatched eggs showed no sign of embryo development (37/74, 50.00%), and most undeveloped eggs were male (36/37, 97.30%). Additional experiments using an incubator suggested that the cause of embryo developmental failure was a lack of developmental ability within the egg, rather than a failure of incubation. This study highlights the importance of clarifying offspring sex ratio at multiple stages and suggests that offspring sex ratio is adjusted after fertilization.     

The plant metabolite, 6-methoxybenzoxazolinone, stimulates an increase in secretion of follicle-stimulating hormone and size of reproductive organs in Microtus pinetorum

The plant metabolite, 6-methoxybenzoxazolinone (6-MBOA), occurring in leaf tissue of rapidly growing monocots, cues reproduction in some mammals. In the pine vole, Microtus pinetorum, peripubertal females respond to this nonestrogenic compound with a 40% increase in serum levels of follicle-stimulating hormone (FSH). In addition, 6-MBOA significantly increases the weight of the ovary and uterus in both peripubertal and mature voles. This study is the first to offer evidence that 6-MBOA interacts with the pituitary to stimulate reproduction in voles.     

Effect of nestbox type on occupancy and breeding biology of Tree Sparrows Passer montanus in central Spain

Avian life-history studies are often conducted on populations nesting in nestboxes. However, the type of nestbox used is a potentially confounding variable, as each model shows specific characteristics. In recent decades, a new commercial model of artificial nestbox made of woodcrete, a mixture of sawdust and additives, has become popular owing to its better protection against predators compared with the classic wooden design. We assess the effect of nestbox type on the breeding ecology of Tree Sparrows Passer montanus , focusing on their thermal properties, an influential factor in nestbox selection. Occupancy rates and reproductive parameters of Tree Sparrows were compared between birds breeding in woodcrete and wooden nestboxes over 5 years. Woodcrete nestboxes had a higher occupancy rate and birds breeding in them had earlier clutches, a shorter incubation period and more reproductive attempts per season than birds nesting in wooden boxes. Clutch size and nestling condition did not differ between nestbox types, but reproductive success was higher in woodcrete nestboxes. The higher temperature in woodcrete nestboxes (1.5 °C higher on average) might explain these differences. Such differences may bias results obtained in comparative studies where more than one nestbox type is used.     

Tissue alterations in Microtus montanus chronically infected with Trypanosoma brucei gambiense

Changes in liver, spleen, kidneys, heart, and brain are reported for Microtus montanus chronically infected with Trypanosoma brucei gambiense. An increase in body weight of infected animals was attributable to a significant increase in total mass of spleen, liver and kidney. Cellular infiltrate consisting primarily of lymphocytes and plasma cells was observed in all organs and was particularly evident in intralobular connective tissue of the liver, adipose tissue of the hilum, and adjacent medullary region of the kidney, spleen, and the meninges. Disruption of normal metabolism and the pathological changes observed in liver and kidney suggest that the survival of trypanosome-infected voles is dependent largely on the physiological response occurring in these organs.     

Effects of inducer pretreatment on liver function and morphology in the mountain vole Microtus montanus

Liver function and morphology of the mountain vole, Microtus montanus, were examined after i.p. injections of phenobarbital, beta-naphthoflavone, or Aroclor 1254 at three dose levels. The results of the liver function tests showed serum glutamic pyruvic transaminase and serum malathion carboxylesterase activities were normal in all the treatment groups. The histological results showed no necrotic tissue but did reveal two different morphological stages related to the level of monooxygenase activity; a low induction state was represented by foamy vacuolated hepatocytes while high induction states were related to enlarged, swollen, hypertrophied cells.     

Multiple alpha-keto aciduria in Microtus montanus chronically infected with Trypanosoma brucei gambiense

Microtus montanus chronically infected with a monomorphic strain of Trypanosoma brucei gambiense excreted in urine greatly elevated quantities of not only the aromatic alpha-keto acids, phenylpyruvic and 4-hydroxyphenylpyruvic acids, but also two aliphatic alpha-keto acids, pyruvic and alpha-ketoglutaric acids. Elevated keto acid excretion began approximately midway through infection and quantities remained elevated until death. Daily keto acid excretion did not correlate with daily parasitemia. Thus, a large metabolic disturbance exists in laboratory animals infected with African trypanosomes. The multiple alpha-keto aciduria potentially contributes to the pathogenesis of chronic African trypanosomiasis.     

Adult sex ratio variation: implications for breeding system evolution

Adult sex ratio (ASR) exhibits immense variation in nature, although neither the causes nor the implications of this variation are fully understood. According to theory, the ASR is expected to influence sex roles and breeding systems, as the rarer sex in the population has more potential partners to mate with than the more common sex. Changes in mate choice, mating systems and parental care suggest that the ASR does influence breeding behaviour, although there is a need for more tests, especially experimental ones. In the context of breeding system evolution, the focus is currently on operational sex ratios (OSRs). We argue that the ASR plays a role of similar importance and urge researchers to study the ASR and the OSR side by side. Finally, we plead for a dynamic view of breeding system evolution with feedbacks between mating, parenting, OSR and ASR on both ecological and evolutionary time scales.