No evidence for selective follicle abortion underlying primary sex ratio adjustment in pigeons

Primary sex ratio adjustment in birds has been extensively studied, yet the underlying physiological mechanisms are far from understood. Avian females are the heterogametic sex (ZW), and the future sex of the offspring is determined at chromosome segregation during meiosis I, shortly before the oocyte is ovulated. Assuming that the mother can detect the sex of the developing oocyte before ovulation, it has been suggested that a follicle of the un-preferred sex could selectively be induced to become atretic and regress instead of being ovulated (selective follicle abortion). This potential mechanism has been proposed to underlie biased primary sex ratios in birds, including the homing pigeon (Columba livia domestica), which produces a modal clutch size of two eggs. However, without replacement by an additional, already mature follicle, abortion of a preovulatory follicle would most likely result in either reduced clutch sizes or laying gaps, since a not-yet-recruited follicle still needed to undergo the whole maturation phase. In the current study we killed female pigeons, which were adjusting embryo sex of first eggs according to change in body mass. We examined ovaries for signs of follicle abortion but did not find any supporting evidence. All females produced one or two mature follicles but only two out of the 56 experimental birds produced an additional third mature follicle. Therefore, our results do not corroborate the hypothesis that pigeon mothers manipulate primary offspring sex by selectively aborting follicles of the un-preferred sex

An adaptive annual rhythm in the sex of first pigeon eggs

When the reproductive value of male and female offspring varies differentially, parents are predicted to adjust the sex ratio of their offspring to maximize their fitness (Trivers and Willard, Science 179:90–92, 1973). Two factors have been repeatedly linked to skews in avian offspring sex ratio. First, laying date can affect offspring sex ratio when the sexes differ in age of first reproduction, such that the more slowly maturing sex is overproduced early in the season. Second, position of the egg in the laying sequence of a clutch may affect sex ratio bias since manipulating the sex of the first eggs may be least costly to the mother. We studied both factors in two non-domesticated pigeon species. Both the Wood pigeon (Columba palumbus) and the Rock pigeon (Columba livia) have long breeding seasons and lay two-egg clutches. In the field, we determined the sex of Wood pigeon nestlings. In Rock pigeons, housed in captivity outdoors, we determined embryo sex after 3 days of incubation. On the basis of their sex-specific age of first reproduction, we predicted that males, maturing at older age than females, should be produced in majority early and females later in the year. This was confirmed for both species. The bias was restricted to first eggs. Rock pigeons produced clutches throughout the year and show that the sex of the first egg followed an annual cycle. To our knowledge, this study presents the first evidence of a full annual rhythm in adaptive sex allocation in birds. We suggest that this reflects an endogenous seasonal program in primary sex ratio controlled by a preovulatory mechanism

High Fat Diet Prevents Over-Crowding Induced Decrease of Sex Ratio in Mice

Adaptive theory predicts that mothers would be advantaged by adjusting the sex ratio of their offspring in relation to their offspring's future reproductive success. In the present study, we tested the effect of housing mice under crowded condition on the sex ratio and whether the fat content of the diet has any influence on the outcome of pregnancies. Three-week-old mice were placed on the control diet (NFD) for 3 weeks. Thereafter the mice were allotted randomly to two groups of 7 cages each with 4, 6, 8, 10, 12, 14, and 16 mice in every cage to create increasing crowding gradient and fed either NFD or high fat diet (HFD). After 4 weeks, dams were bred and outcomes of pregnancy were analyzed. The average dam body weight (DBW) at conception, litter size (LS) and SR were significantly higher in HFD fed dams. Further, male biased litters declined with increasing crowding in NFD group but not in HFD. The LS and SR in NFD declined significantly with increasing crowding, whereas only LS was reduced in HFD group. We conclude that female mice housed under overcrowding conditions shift offspring SR in favor of daughters in consistent with the TW hypothesis and high fat diet reduces this influence of overcrowding

Evidence for Mito-Nuclear and Sex-Linked Reproductive Barriers between the Hybrid Italian Sparrow and Its Parent Species

Studies of reproductive isolation between homoploid hybrid species and their parent species have rarely been carried out. Here we investigate reproductive barriers between a recently recognized hybrid bird species, the Italian sparrow Passer italiae and its parent species, the house sparrow P. domesticus and Spanish sparrow P. hispaniolensis. Reproductive barriers can be difficult to study in hybrid species due to lack of geographical contact between taxa. However, the Italian sparrow lives parapatrically with the house sparrow and both sympatrically and parapatrically with the Spanish sparrow. Through whole-transcriptome sequencing of six individuals of each of the two parent species we identified a set of putatively parent species-diagnostic single nucleotide polymorphism (SNP) markers. After filtering for coverage, genotyping success (>97%) and multiple SNPs per gene, we retained 86 species-informative, genic, nuclear and mitochondrial SNP markers from 84 genes for analysis of 612 male individuals. We show that a disproportionately large number of sex-linked genes, as well as the mitochondria and nuclear genes with mitochondrial function, exhibit sharp clines at the boundaries between the hybrid and the parent species, suggesting a role for mito-nuclear and sex-linked incompatibilities in forming reproductive barriers. We suggest that genomic conflict via interactions between mitochondria and sex-linked genes with mitochondrial function ("mother's curse") at one boundary and centromeric drive at the other may best explain our findings. Hybrid speciation in the Italian sparrow may therefore be influenced by mechanisms similar to those involved in non-hybrid speciation, but with the formation of two geographically separated species boundaries instead of one. Spanish sparrow alleles at some loci have spread north to form reproductive barriers with house sparrows, while house sparrow alleles at different loci, including some on the same chromosome, have spread in the opposite direction to form barriers against Spanish sparrows

Maternal condition but not corticosterone is linked to brood sex ratio adjustment in a passerine bird

There is evidence of offspring sex ratio adjustment in a range of species, but the potential mechanisms remain largely unknown. Elevated maternal corticosterone (CORT) is associated with factors that can favour brood sex ratio adjustment, such as reduced maternal condition, food availability and partner attractiveness. Therefore, the steroid hormone has been suggested to play a key role in sex ratio manipulation. However, despite correlative and causal evidence CORT is linked to sex ratio manipulation in some avian species, the timing of adjustment varies between studies. Consequently, whether CORT is consistently involved in sex-ratio adjustment, and how the hormone acts as a mechanism for this adjustment remains unclear. Here we measured maternal baseline CORT and body condition in free-living blue tits (Cyanistes caeruleus) over three years and related these factors to brood sex ratio and nestling quality. In addition, a non-invasive technique was employed to experimentally elevate maternal CORT during egg laying, and its effects upon sex ratio and nestling quality were measured. We found that maternal CORT was not correlated with brood sex ratio, but mothers with elevated CORT fledged lighter offspring. Also, experimental elevation of maternal CORT did not influence brood sex ratio or nestling quality. In one year, mothers in superior body condition produced male biased broods, and maternal condition was positively correlated with both nestling mass and growth rate in all years. Unlike previous studies maternal condition was not correlated with maternal CORT. This study provides evidence that maternal condition is linked to brood sex ratio manipulation in blue tits. However, maternal baseline CORT may not be the mechanistic link between the maternal condition and sex ratio adjustment. Overall, this study serves to highlight the complexity of sex ratio adjustment in birds and the difficulties associated with identifying sex biasing mechanisms

Developmental programming: the role of growth hormone

Developmental programming of the fetus has consequences for physiologic responses in the offspring as an adult and, more recently, is implicated in the expression of altered phenotypes of future generations. Some phenotypes, such as fertility, bone strength, and adiposity are highly relevant to food animal production and in utero factors that impinge on those traits are vital to understand. A key systemic regulatory hormone is growth hormone (GH), which has a developmental role in virtually all tissues and organs. This review catalogs the impact of GH on tissue programming and how perturbations early in development influence GH function

Particle identification in ALICE : a Bayesian approach

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