Behavioral and endocrine correlates of multiple brooding in the semicolonial house sparrow Passer domesticus. II. Females

Behavioral and endocrine changes associated with reproductive events were studied in free-living female house sparrows (Passer domesticus). Circulating levels of luteinizing hormone (LH) and estradiol (E2) were maximal during egg-laying, declined during incubation, and began to rise during the nestling stage. This pattern was repeated three to five times during the prolonged breeding season of this species. Multivariate statistical analysis demonstrated that elevated levels of LH and E2 were associated with maximal sexual activity, high rates of intrusion at nests by conspecifics, and elevated rates of agonistic activity. Patterns of sexual activity varied during the season and perhaps reflected differing strategies for protecting paternity adopted by the male. Curiously, elevated levels of testosterone (T) and dihydrotestosterone (DHT) were not associated with high levels of intrusion or agonistic response, but rather were associated with incubation stages. As in males, concentrations of corticosterone (B) were high during each egg-laying and nestling stage and were associated with high or rising levels of reproductive hormones, suggesting that reproductive activity was not overly stressful to these birds. Body mass and fat depots declined during the season and may regulate termination of reproduction. It appears that access to abundant food resources found in association with human dwellings allows house sparrows to maintain reproductive activity longer than most other temperate-zone dwelling bird species.     

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.     

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...     

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.     

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.     

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.     

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.

     

Uropygial gland size correlates with feather holes,body condition and wingbar size in the house sparrow Passer domesticus

The uropygial gland is an organ exclusive of birds that secretes an oily substance, the uropygial secretion, the functions of which are still debated. One of the proposed hypothesis is its possible action against chewing lice (order Phthiraptera), a group of avian ectoparasites that feed on feathers, causing different types of harm. However, this hypothesis lacks support. The present study analyses the relationship between uropygial gland size and the number of feather holes (which is correlated with the load of chewing lice) in the house sparrow Passer domesticus. Moreover, the relationship between the uropygial gland size and different aspects of sparrow health (body condition, immunocompetence and haematocrit), as well as sexually selected traits in males (badge and wingbar size), is tested. The results show a negative correlation between uropygial gland size and number of feather holes, a result found both years of the study. This result supports the hypothesis that uropygial secretion is used against chewing lice. Uropygial gland size also correlated positively with body condition (residuals of body mass relative to tarsus length) and immunocompetence, being therefore related to bird health. After a year in captivity, with resources provided ad libitum, no correlation was found between individual uropygial gland size and body condition or haematocrit, perhaps because the negative effect that chewing lice exert on bird health was offset by captivity conditions. Uropygial gland size was not correlated with badge size, but it was correlated with wingbar size, which furthermore supports the contention that this sexually selected signal acts as an indicator of lice resistance in the house sparrow. In summary, this study supports the idea of a positive relationship between uropygial gland and bird health in the house sparrow, the gland secretion affording resistance against chewing lice.     

Malaria infection negatively affects feather growth rate in the house sparrow Passer domesticus

Birds often face various stressors during feather renewing, for example, enduring infection with blood parasites. Because nutritional resources are typically limited, especially for wild animals, when an individual allocates energy to one physiological system, there is subsequently less for other processes, thereby requiring a trade‐off. Surprisingly, potential trade‐offs between malaria infection and feather growth rate have not been experimentally considered yet. Here, we conducted three studies to investigate whether a trade‐off occurs among feather growth rate, malaria infection and host health conditions. First, we explored whether naturally infected and uninfected house sparrows differed in feather growth rate in the wild. Second, we asked whether experimental inoculation of malaria parasites and/or forcing the renewal of a tail feather. Lastly, we evaluated whether individual condition was affected by experimentally‐induced feather regrowth and/or malaria experimental infection. Our findings showed that feather growth rate was negatively affected by natural malaria infection status in free‐living birds and by experimental infection in captive birds. Furthermore, birds that did not increase body mass or hematocrit during the experimental study had slower feather growth. Together our results suggest that infection with blood parasites has more negative health effects than the growth of tail feathers and that these two processes (response to blood parasite infection and renewal of feathers) are traded‐off against each other. As such, our results highlight the role of malaria parasites as a potential mechanism driving other trade‐offs in wild passerines.     

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.     

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.     

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.     

Genetic variation in the house sparrow, Passer domesticus, in the East Midlands of England

A series of 15 samples of house sparrows taken in the East Midlands of England were screened for 14 variable and 9 invariable enzyme loci. The gene frequency data were analysed both for heterozygosity and genetic identity using Nei's and Roger's statistics. There is a cline in heterozygosity northwards across the region, and populations are closely similar. The differentiation observed is very close to that expected for a continuously distributed species with a neighbourhood area of 8.9 km² and effective population size of 999.6.