Cytological steps during spermiogenesis in the house sparrow (Passer domesticus,Linnaeus)

Spermiogenesis of the domestic sparrow was investigated with the light and electron microscopes and a step by step classification is proposed. Three cell populations corresponding to early, mid and late spermatids were easily divided according to their positions in the seminiferous epithelium. In addition to this initial separation, six steps were recognized, based on nuclear morphology and the degree of chromatin condensation, in association to their acrosomal and flagellar development. Early spermiogenesis is the period previous to chromatin condensation. The first step can be recognized by the extending flagellum and the second by the pro-acrosome development in contact with the nucleus. During the third or intermediate step, chromatin condenses and the cell becomes polarized with the pro-acrosomic vesicle and the tail occupying opposite sides of the nucleus. Late spermiogenesis, including steps IV-VI, is marked by complete chromatin condensation. The final cellular modifications lead to the formation of a spiraled spermatozoon. This shape is due to the twisting of the acrosome and nucleus, as well as the helical arrangement of mitochondria around the axoneme along most of the flagellum, making an exceptionally long middle piece.     

Adenosine deaminase polymorphism in the house sparrow, Passer domesticus

A polymorphism at the adenosine deaminase locus of the house sparrow, Passer domesticus, has been investigated by starch gel electrophoresis. Five alleles have been identified, and most populations seem to be close to the Hardy-Weinberg equilibrium. The allele frequencies differ strikingly across Europe, and in Britian there are significant differences between urban and rural populations. Samples from introduced populations in Australia and New Zealand lack some of the rarer alleles, as predicted from the Founder Effect.     

Blood oxygen transport in the house sparrow,Passer domesticus

Journal of Comparative Physiology B - Oxygen equilibrium curves (O2EC's) were generated for the adult house sparrowPasser domesticus at temperatures from 35 to 45 °C using a thin blood...     

Plasmodium relictum infection and MHC diversity in the house sparrow (Passer domesticus)

Antagonistic coevolution between hosts and parasites has been proposed as a mechanism maintaining genetic diversity in both host and parasite populations. In particular, the high level of genetic diversity usually observed at the major histocompatibility complex (MHC) is generally thought to be maintained by parasite-driven selection. Among the possible ways through which parasites can maintain MHC diversity, diversifying selection has received relatively less attention. This hypothesis is based on the idea that parasites exert spatially variable selection pressures because of heterogeneity in parasite genetic structure, abundance or virulence. Variable selection pressures should select for different host allelic lineages resulting in population-specific associations between MHC alleles and risk of infection. In this study, we took advantage of a large survey of avian malaria in 13 populations of the house sparrow (Passer domesticus) to test this hypothesis. We found that (i) several MHC alleles were either associated with increased or decreased risk to be infected with Plasmodium relictum, (ii) the effects were population specific, and (iii) some alleles had antagonistic effects across populations. Overall, these results support the hypothesis that diversifying selection in space can maintain MHC variation and suggest a pattern of local adaptation where MHC alleles are selected at the local host population level.     

New polymorphic microsatellite loci in the house sparrow, Passer domesticus

We developed 13 new polymorphic microsatellite loci in the house sparrow (Passer domesticus), which exhibited from 2 to 15 alleles. Observed and expected heterozygosities ranged from 0.17 to 0.77 and from 0.35 to 0.85, respectively. We detected no linkage disequilibrium between loci. Allele frequencies supported Hardy-Weinberg equilibrium for 8 loci out of 13 after Bonferroni correction. Combined with loci previously isolated in the house sparrow, these new microsatellite markers provide valuable tools to study population genetics of this species.     

Renal response to dietary protein in the house sparrow Passer domesticus

Many birds switch seasonally or during ontogeny between diets of varying protein content. In mammals, high-protein diets induce hypertrophy of the kidney in general and of the thick ascending limbs (TAL) in particular, along with increases in glomerular filtration rate (GFR) and urine flow. A hypothesis to explain these phenomena is that the TAL become increasingly sensitive to peptide hormones (glucagon and antidiuretic hormone [ADH]) released in response to protein feeding; the consequent enhancement of ion reabsorption dilutes urine reaching the macula densa, thereby suppressing tubulo-glomerular feedback (TGF) and causing a rise in GFR. Avian kidneys possess most of the elements involved in this mechanism, including loops of Henle with TAL, sensitivity of TAL to ADH (arginine vasotocin [AVT] in birds), and the elements of TGF. We therefore hypothesized that switching from a low-protein to a high-protein diet would induce responses in birds similar to those found in mammals. We tested this hypothesis by feeding house sparrows, Passer domesticus, isocaloric diets containing either 8% or 30% protein. Birds on high-protein food had larger renal medullae, both in mass and in TAL diameter, but no increase in whole-kidney mass. Urine flow was approximately doubled on high-protein food, but there was no change in GFR. We were not able to detect an increased sensitivity of AVT-induced adenylyl cyclase activity in TAL from high-protein animals, and responsiveness to glucagon was higher in TAL from birds eating low-protein food. We are unable to conclude that a suppression of TGF is responsible for the rise in urine flow in birds eating high-protein foods, and the mechanisms behind the medullary hypertrophy and the diuresis remain to be fully explored.     

Diversifying selection on MHC class I in the house sparrow (Passer domesticus)

Genes of the major histocompatibility complex (MHC) are the most polymorphic loci known in vertebrates. Two main hypotheses have been put forward to explain the maintenance of MHC diversity: pathogen-mediated selection and MHC-based mate choice. Host–parasite interactions can maintain MHC diversity via frequency-dependent selection, heterozygote advantage, and diversifying selection (spatially and/or temporally heterogeneous selection). In this study, we wished to investigate the nature of selection acting on the MHC class I across spatially structured populations of house sparrows ( Passer domesticus ) in France. To infer the nature of the selection, we compared patterns of population differentiation based on two types of molecular markers: MHC class I and microsatellites. This allowed us to test whether the observed differentiation at MHC genes merely reflects demographic and/or stochastic processes. At the global scale, diversifying selection seems to be the main factor maintaining MHC diversity in the house sparrow. We found that (i) overall population differentiation at MHC was stronger than for microsatellites, (ii) MHC marker showed significant isolation by distance. In addition, the slope of the regression of F _ST on geographical distance was significantly steeper for MHC than for microsatellites due to a stronger pairwise differentiation between populations located at large geographical distances. These results are in agreement with the hypothesis that spatially heterogeneous selective pressures maintain different MHC alleles at local scales, possibly resulting in local adaptation.     

Patterns of hatching failure in the house sparrow Passer domesticus

Hatching failure is widespread in birds despite presumably strong selection against any wasted reproductive effort and yet there have been few attempts at uncovering sources of variation in failure within a species. Here we use 11 yr of data on the frequency of both undeveloped and unhatched eggs in a marked population of house sparrows Passer domesticus to examine the effects of multiple factors hypothesized to affect hatching success in birds including parental identity, phenotype and genotype, as well as several environmental variables. Unhatched eggs were present in 34.3% of 1523 clutches in which at least one egg hatched, and a total of 10.1% of eggs failed to hatch, of which 75.7% had no visible embryo. We found an effect of female identity on the proportion of eggs that developed and an effect of male identity on hatching success, as well as a positive effect of egg size on both the proportion of eggs that developed and hatching success between females. Neither the proportion of eggs that developed nor hatching success varied according to time of season or weather conditions, clutch size, the age of either parent, the size of the male's black bib, female size, female heterozygosity or the genetic similarity between members of a pair. There was also no positional bias in the occurrence of undeveloped eggs, although undeveloped eggs were more common among birds nesting at low density. Our results suggest that hatching failure in house sparrows has few environmental components and is primarily influenced by intrinsic differences among individuals.     

Fourteen polymorphic microsatellite loci characterized in the house sparrow Passer domesticus (Passeridae,Aves)

We characterized 14 polymorphic microsatellite loci in the house sparrow Passer domesticus. Four loci were isolated from house sparrow genomic libraries and 10 loci were identified by testing 100 loci that had been originally isolated in other passerine species. Loci were characterized in 37–54 unrelated sparrows from British and Norwegian populations. Each locus displayed between two and 31 alleles, with the observed heterozygosity ranging between 0.30 and 0.91.     

No evidence for differential maternal allocation to offspring in the house sparrow (Passer domesticus)

We tested the differential maternal allocation hypothesis ina population of house sparrows. We experimentally altered theattractiveness of males by treating them with implants filledwith crystalline testosterone (T) or left empty (C). We subsequentlymonitored maternal investment as a function of male hormonaltreatment and the size of the black patch of feathers on thethroat (i.e., the badge), a sexually selected trait. The differentialallocation hypothesis predicts that females should adjust theirinvestment with respect to the benefits they receive by matingwith an attractive male. Given that both circulating levelsof T and badge size are condition-dependent traits, we expectedthat females mated with T males and/or with large-badged malesshould invest more into current reproduction. Contrary to thisprediction, we found no evidence that suggested differentialmaternal allocation in this population of house sparrows. Femaleinvestment in yolk T, yolk mass, clutch size, chick brooding,and feeding was not affected by male hormonal treatment or bymale badge size. As expected, T males invested less into chickbrooding and feeding. More surprisingly, females did not compensatethe reduced paternal contribution to chick feeding. As a consequence,the breeding success of T pairs was largely reduced comparedwith that of C pairs. The absence of differential allocationin a system in which it could have an adaptive role raises thequestion about the possible constraints or overriding factorsoperating on patterns of reproductive investment in this species.     

Temperature regulation and metabolic rhythms in populations of the house sparrow,Passer domesticus

• 1.1. The house sparrow, Passer domesticus, has a circadian rhthym of metabolism and body temperature.
• 2.2. Evolutionary adaptation to a hot and humid climate is reflected in the lower metabolism and greater insulation of the Houston population than observed in populations from Ann Arbor, Michigan; Boulder, Colorado and Syracuse, New York.
• 3.3. There are no significant differences in either body temperature or evaporative water loss of all four populations.
• 4.4. The Houston population is able to survive higher ambient temperatures than is found in the Ann Arbor, Michigan or Boulder, Colorado population.

     

The role of testosterone in bib size determination in the male house sparrow Passer domesticus,is age dependent

Secondary sexual signals are thought to indicate individual quality. In order to understand the evolutionary pressures that give rise to such traits it is important to understand the physiological mechanisms underlying their production. The black bib of the house sparrow Passer domesticus is known to function as a badge of social status in males. Past studies have found that the size of the bib in older males is determined, at least partly, by the androgen testosterone. The immunocompetence handicap hypothesis suggests that testosterone has a key role in maintaining honest signalling – it is both involved in the development or expression of sexual signals and is immunosuppressive. In this paper we test experimentally two hypo theses relating to bib size development, whether 1) testosterone is only immunosuppressive in conditions where the natural feedback loop from the testes has been removed, and 2) testosterone is, in addition to influencing the bib size of older males, responsible for the size of the bib in juvenile sparrows. In the first experiment we found that exogenous testosterone administered to intact males during the winter (when LH and FSH levels are very low and were not artificially increased by castration) caused significant immunosuppression, albeit in interaction with the stress hormone corticosterone. Second, we found that exogenous testosterone administration in castrated fledgling male house sparrows had no effect on subsequent post‐juvenile moult bib size relative to controls. Our results suggest that in some circumstances testosterone can be immunosuppressive, but that its role in bib size determination is age‐dependent.     

Correlates of egg size variation in a population of house sparrow Passer domesticus

Propagule size represents an important life-history trait under maternal control. Despite a positive relationship between propagule size and components of fitness, propagule size displays tremendous amounts of variation which causes are poorly understood within natural populations. With a study of a house sparrows Passer domesticus, we investigate maternal and environmental correlates of egg size, quantify variation in egg size within and between females and broods, and estimate heritability. Egg size had a curvilinear relationship with clutch size and decreased significantly in subsequent broods within seasons. Furthermore, egg size increased with maternal body mass, was positively affected by spring temperatures and curvilinearly related to temperature during the 2 weeks prior to egg laying. Some 46.4 % of variation in egg size was due to differences between females, and 21.9 % was explained by variation between broods by the same female. The heritability of egg size was low (h ² = 0.26) compared to estimates from other studies (h ² > 0.6). The present study challenges the recent idea that egg size is an inflexible maternal characteristic with very high additive genetic variance, and suggests that females are subject to both intrinsic and extrinsic constraints prior to and during egg formation, leading to the observed plasticity in egg size. In a general sense, propagule size could be expected to be both limited by and adaptively adjusted in accordance to prevailing environmental conditions.     

Variation in MHC genotypes in two populations of house sparrow (Passer domesticus) with different population histories

Small populations are likely to have a low genetic ability for disease resistance due to loss of genetic variation through inbreeding and genetic drift. In vertebrates, the highest genetic diversity of the immune system is located at genes within the major histocompatibility complex (MHC). Interestingly, parasite‐mediated selection is thought to potentially maintain variation at MHC loci even in populations that are monomorphic at other loci. Therefore, general loss of genetic variation in the genome may not necessarily be associated with low variation at MHC loci. We evaluated inter‐ and intrapopulation variation in MHC genotypes between an inbred (Aldra) and a relatively outbred population (Hestmannøy) of house sparrows (Passer domesticus) in a metapopulation at Helgeland, Norway. Genomic (gDNA) and transcribed (cDNA) alleles of functional MHC class I and IIB loci, along with neutral noncoding microsatellite markers, were analyzed to obtain relevant estimates of genetic variation. We found lower allelic richness in microsatellites in the inbred population, but high genetic variation in MHC class I and IIB loci in both populations. This suggests that also the inbred population could be under balancing selection to maintain genetic variation for pathogen resistance.