Variation in genetic diversity of tree sparrow (Passer montanus) population in long-term environmental heavy metal polluted areas.

Genetic diversity is the bedrock of evolution. The "Genetic Erosion" hypothesis posits that environmental pollution could cause reduced genetic diversity. To explore the effects of heavy metal pollution on genetic diversity in natural populations, we selected an area with more than sixty years of heavy metal contamination (Baiyin, BY) and a relatively unpolluted one (Liujiaxia, LJX), and tree sparrow (Passer montanus) as study models. Five tree sparrow populations were sampled in BY at sites differing in heavy metal pollution level. Lower genetic diversity based on seven microsatellite loci was observed in the five tree sparrow populations from BY compared with those from LJX. Analysis of molecular variance indicated no significant genetic differentiation between BY and LJX. However, the observed heterozygosity and allelic richness were negatively correlated to the lead and cadmium concentrations in the primary feathers of tree sparrow. Our results indicated the genetic diversity might have a negative response to long-term environmental heavy metal pollution in tree sparrow, supporting the "Genetic Erosion" hypothesis. Therefore, the findings shed lights on the possible effects of heavy metal pollution on genetic diversity of wild bird populations.

Yang W ，Ding J ，Wang S ，Yang Y ，Song G ，Zhang Y ... -  《-》

Effects of environmental metal pollution on reproduction of a free-living resident songbird, the tree sparrow (Passer montanus).

Anthropogenic metal pollution is known to adversely affect bird reproduction; however, few systematic studies are available on the effects of metal pollution on breeding performance and parental investment in a common resident songbird, the tree sparrow (Passer montanus). We conducted this study in two sites, a long-term heavy metal polluted site (Baiyin [BY]) and a relatively unpolluted site at approximately 110 km distance (Liujiaxia [LJX]), to assess the potential effects of environmental metal contamination on breeding parameters (clutch size, hatching success, fledging success, and growth of nestlings) and parental investment. The results showed smaller clutch size, lower fledging success, and differences in incubation behaviors of tree sparrows in BY than in LJX. Although there was no difference in parental body condition (residual body mass) between the two study sites, the parents responded differently with respect to reproduction due to varying metal levels in their habitats and bodies. Higher Cd levels in the primary feathers of females in BY were associated with lower clutch sizes. Parental investment including incubation duration and feeding rates showed no significant difference between the two sites during the incubation and nestling periods, but the frequencies of incubation visits were higher in BY. Parental behavior during the incubation period was also negatively affected by the parental Pb and Cd levels. Although the nestling growth patterns were relatively similar between the two sites, the nestlings were smaller, had lower body weight, and fledged later and fledging rate was also lower in BY than in LJX. Metal concentrations were higher in nestling organs and feces in BY. Taken together, metal pollution might adversely affect nestling growth condition. Our results suggest a negative response in the reproduction of tree sparrows to long-term environmental metal pollution.

Ding J ，Yang W ，Wang S ，Zhang H ，Yang Y ，Bao X ，Zhang Y ... -  《-》

Does environmental metal pollution affect bird morphometry? A case study on the tree sparrow Passer montanus.

Morphological characteristics are the leading indicators of the health status of birds. To explore the effects of heavy metals on bird morphometry in natural populations, tree sparrows (Passer montanus) were studied in a polluted site [Baiyin (BY)] and a relatively unpolluted site [Liujiaxia (LJX)]. This study aimed to examine whether morphological variables, the fluctuating asymmetry (FA) of the wing, tarsus, and toe length, were associated with heavy metals (Cu, Zn, Pb, and Cd) and Ca levels in different tissues and feces of adults and nestlings. Results showed that adults collected from BY contained relatively higher heavy metal concentrations and lower Ca concentrations in different tissues than those from LJX. Smaller body sizes and higher FA levels of adults and nestlings were found in BY than in LJX. Although higher heavy metal concentrations in some tissues were associated with smaller morphological characteristics of adults, the effects were not obvious in nestlings. The most correlated heavy metal with as many characteristics was heavy metal in primary feather in both sites, and the most affected characteristic was body mass in BY. The FA values of adults and nestlings in BY were positively affected by heavy metal concentrations in different tissues and feces. The growth rate of wing and tarsus length of nestlings in BY were negatively affected by the FA values of wing and tarsus length, respectively. Taken together, environmental metal pollution might affect the morphological characteristics of tree sparrows. These findings suggest that the morphological characteristics of tree sparrows, especially FA, can be used as indicators of metal pollution, underscoring the importance of measuring morphological characteristics in avian ecotoxicology field studies.

Ding J ，Yang W ，Wang S ，Zhang H ，Zhang Y ... -  《-》

Improvement of sperm traits related to the high level of extra-pair fertilization in tree sparrow population under long-term environmental heavy metal pollution.

Environmental stress can affect sperm traits whose changes have been reported to be associated with extra-pair fertilization (EPF) level in natural animal populations. However, little is known regarding how exposure to environmental heavy metals influences sperm traits and EPF level in free-living bird populations. In a previous study, we found that a tree sparrow (Passer montanus) population that has been exposed to heavy metal pollution over 60 years (Baiyin, BY) exhibits increased sperm quality compared with a population from a relatively unpolluted area (Liujiaxia, LJX). The high sperm quality could be related to extra-pair mating rates. Therefore, the present study investigated EPF level (the ratio of extra-pair offspring) in tree sparrow populations from BY and LJX, and analyzed the relationship between sperm traits (morphology, velocity and quantity) and EPF success. EPF success of tree sparrows was significantly correlated with their sperm velocity (p = 0.048) and total sperm length (p = 0.045), indicating that these sperm traits were important for EPF success. Tree sparrows from the BY population produced longer sperm with lower head/flagellum ratio and faster swimming sperm and showed a significantly higher EPF level than conspecifics from LJX. Thus, adaptive variation of sperm characteristics was related to the high EPF level in tree sparrows under long-term environmental heavy metal pollution. The findings are of scientific significance for exploring the evolution of mating tactics in wild bird populations under environmental stress.

Yang W ，Wang S ，Yang Y ，Shen Y ，Zhang Y ... -  《-》

Response of male reproductive function to environmental heavy metal pollution in a free-living passerine bird, Passer montanus.

Heavy metals affect male reproductive function by impairing reproductive organs, disturbing reproductive hormone levels or directly affecting sperm quality. However, little attention has been given to the effect of environmental heavy metals on reproductive function in wild male birds. The present study investigated the alterations of reproductive function in male tree sparrows (Passer montanus) exposed to environments contaminated by heavy metals in terms of testis parameters, reproductive hormone levels and sperm movement characteristics. Two plots, Baiyin (BY, mainly polluted by copper, zinc, lead and cadmium) and Liujiaxia (LJX, a relatively unpolluted area) were selected as sampling sites. The results showed that tree sparrows from BY (1) accumulated higher levels of cadmium in the testes, (2) showed lower superoxide dismutase (SOD) activity and malondialdehyde level, with higher total antioxidant capacity and apoptosis level in the testes, (3) showed higher plasma levels of estrogen, follicle stimulating hormone and luteinizing hormone (LH), and (4) had better sperm movement performance. Additionally, we found that testis size, SOD activity in testes and LH levels were decisive factors in sperm movement performance in tree sparrows. Heavy metal concentrations in testes negatively correlated with testis size, SOD activity in testes, and estrogen levels in tree sparrows. The present study indicates that heavy metals accumulating in testes of tree sparrows adversely affected some key indicators of male reproductive function. However, testicular function, reproductive hormone levels and sperm quality showed adaptive responses that tended to partially compensate for the negative effects in the heavy metal polluted area. This study further indicated that the regulation of testicular function and reproductive hormone levels was the main factor for better sperm quality in tree sparrows exposed to environments contaminated by heavy metals.

Yang Y ，Zhang W ，Wang S ，Zhang H ，Zhang Y ... -  《-》