Effects of testosterone on male-male competition and male-female interactions in blue tits

In temperate-zone birds, testosterone (T) influences male behavior during the breeding season. The elevation of plasma levels of T to a breeding baseline is necessary for basic reproductive behaviors, but it is still unclear whether variation in T levels above this critical threshold influences the intensity of these behaviors. Such a relationship between T and sexually selected traits is a critical assumption of the immunocompetence handicap hypothesis. We here experimentally elevated T levels in blue-tit males above the natural mean (T-males) during the period of nest building and egg laying, without manipulating hormone levels during chick feeding. T-males neither interacted more often with other males, nor did they respond more aggressively to a dummy intruder, compared to males with control implants. T-males did not guard their social mates more closely, but they were more likely to interact with potential extra-pair mates. Females mated to T-males did not change their behavior during egg laying and the treatment did not significantly affect male and female feeding rates. Despite this, nests of T-males produced larger and heavier fledglings in one study year. Our observations suggest that T levels above the natural mean during the mating period do not increase aggressive or territorial behavior in male blue tits. However, if females perceived T-males as high-quality mating partners, superior offspring development in nests of T-males might be caused by higher maternal investment. Hence, male behaviors involved in mate attraction may have been influenced by T levels above the natural mean.Communicated by R. Gibson     

Mate choice in the yellow-shouldered widowbird: correlates of male attractiveness

Recent investigations of male ornaments in sexual selection have used experimental manipulation of tail length in three widowbird species, but only for one of these have correlates of male reproductive success been reported. I examined correlates of male attractiveness to nesting females over two breeding seasons for the polygynous yellow-shouldered widowbird, Euplectes macrourus, in order to discover which cues females may be using to select mates. The black, long-tailed ( 10 cm) males defend large territories and build nest frames, or cock's nests, which females then line and use for nesting. I examined various aspects of male morphology, five behavioral displays, territory characteristics, and the number of cock's nests that males built. Few correlates of mating success were found. The best predictor was the number of cock's nests that a male builds, though one courtship display also correlated with male mating success in 1 year, as did average grass height. Tail length did not correlate with male mating success. A partial correlation analysis confirmed that cock's nests and, in 1 year, grass height, were the primary contributers to male success. Females may choose where to nest primarily on the availability of suitable nesting sites. Long tails may be used by females seeking extra-pair copulations or in male-male competition for territories.     

含硫及含氯化肥对湘南水田土壤酸度和养分有效性的影响

1990年5—11月,在湖南祁阳中国农科院红壤实验站水稻田布置田间试验,研究结果证实,在早稻和晚稻生长期间,与含氯化肥相比,施含硫化肥更能降低土壤pH而使土壤酸化,因而在南方水田施用含硫化肥时,必须和石灰及生理碱性肥相配合。同时,施含硫化肥能提高土壤有效性磷和钾的含量,增强土壤保肥与供肥能力。对大田水样中养分离子监测的结果表明,施含硫化肥减少钾离子的淋失;而施含氯化肥则减少硝态氮的淋溶,提高水田氮肥的利用率。     

Dominance rank,resource availability,and reproductive maturation in female savanna baboons

Summary Ten years of data collected from a population of savanna baboons, Papio cynocephalus anubis, residing near Gilgil, Kenya were analyzed to ascertain the extent to which social and ecological factors influence reproductive maturation in females. First sexual swelling occurred at an average age of 4.79 years and first birth occurred at an average age of 6.92 years. Age at first menses was significantly correlated with age at first sexual swelling, but age at first sexual swelling was not a good predictor of age at first birth. The amount of rainfall in the 6 months preceding first sexual swelling and resource availability were significantly correlated with age at first sexual swelling. When ecological factors were taken into account, dominant females had an earlier age at onset of puberty, but not an earlier age at first birth, than did subordinate females. We suggest that nutritional and social stress operate at the same physiological level to disrupt GnRH pulsatility and retard reproductive maturation in some females. Given that socioecological variables modify the timing of life history events related to fitness in female baboons, the task for the future is to unravel how socioecological factors influence different life history components and generate variation in lifetime reproductive success. Correspondence to: F.B. Bercovitch     

Changes in singing behavior of male black-capped chickadees (Parus atricapillus) following mate removal

We removed the mates of ten male black-capped chickadees (Pares atricapillus) during the nest-building period to determine the effect of female presence on dawn singing. During the first dawn chorus following mate removal, males sang significantly longer, increased movement within their territory, and increased the percentage of their territory covered while singing. After the female was returned, these parameters returned to the pre-removal values. Males did not alter the frequency range or modal frequency of their songs when the mate was removed, nor did they change the degree of frequency shifting in the fee-bee song. We conclude that dawn singing in the black-capped chickadee acts, in part, as an intersexual signal, and that the behavior of frequency shifting in the song may be directed more toward rival males than females. Correspondence to: K. Otter     

Male moths undertake both pre- and in-copulation mate choice based on female age and weight

Variation in reproductive potential usually occurs among individuals of both sexes; for example, some individuals may carry more gametes or be able to continue to generate more gametes in their reproductive life than others. Therefore, to maximize their reproductive success, both sexes are expected to show adaptations for mate choice. However, most authors concentrated on how females choose their mates with the belief that females invest more in reproduction than males, and males are generally eager to pair with any female. In this paper, we report our work on a polygamous moth, Ephestia kuehniella Zeller (Lepidoptera: Pyralidae), with special emphasis on male pre- and in-copulation mate choice in relation to the reproductive quality and re-copulation potential of females. We show that in E. kuehniella, younger and heavier females have significantly higher reproductive value than older and lighter ones, and male sperm supply significantly decreases over successive copulations. Males exercise pre-copulation mate choice by selecting females with higher reproductive potential for copulation and in-copulation mate choice by allocating more sperm to females with higher reproductive potential. However, high-quality females are more likely to re-copulate than low-quality ones, and allocation of more sperm to females by males does not increase female reproductive outputs. It is suggested that the allocation of more sperm to high-quality females functions to increase sperm competitiveness against rivals.     

Body size preferences in the pot-bellied seahorse <Emphasis Type="Italic">Hippocampus abdominalis:</Emphasis> choosy males and indiscriminate females

Male seahorses (genus Hippocampus) provide all post-fertilization parental care, yet despite high levels of paternal investment, these species have long been thought to have conventional sex roles, with female mate choice and male–male competition. Recent studies of the pot-bellied seahorse (Hippocampus abdominalis) have shown that sex-role reversal occurs in high-density female-biased populations, indicating that male mating preferences may lead to sexual selection on females in this species. Egg size, egg number, and offspring size all correlate positively with female body size in Hippocampus, and by choosing large mating partners, male seahorses may increase their reproductive success. While male brood size is also positively correlated with body size, small H. abdominalis males can carry exceptionally large broods, suggesting that the fecundity benefits of female preference for large partners may be limited. We investigated the importance of body size in reproductive decisions of H. abdominalis, presenting focal individuals of both sexes with potential mating partners of different sizes. Mating preferences were quantified in terms of time spent courting each potential partner. Male seahorses were highly active throughout the mate-choice trials and showed a clear behavioral preference for large partners, while females showed significantly lower levels of activity and equivocal mating preferences. The strong male preferences for large females demonstrated here suggest that sexual selection may act strongly on female body size in wild populations of H. abdominalis, consistent with predictions on the importance of female body size for reproductive output in this species. An erratum to this article can be found at     

Assessment of Water Availability and Scarcity Based on Hydrologic Components in an Irrigated Agricultural Watershed Using SWAT

This study assesses the water availability and the water scarcity based on the hydrologic behavior under different weather conditions and crop coverages in an irrigated agricultural area of Rincon Valley in New Mexico using the SWAT (Soil and Water Assessment Tool) model. Two spatial crop coverages included normal (2008) and dry (2011) years with 14 different crop sets for each year. The SWAT was applied to generate the five essential indicators (surface flow, evapotranspiration, soil water, groundwater recharge, and irrigation water) to evaluate the integrated water availability based on hydrologic response units (HRUs) along with the Arrey Canal to supply irrigation water in the crop areas. The water availability index scores (0–1 range with 1 being the most available and 0 the least available) of alfalfa, corn, cotton, and pecans were 0.21, 0.56, 0.91, and 0.20, respectively, in the normal year and 0.16, 0.78, 0.88, and 0.24, respectively, in the dry year. In the dry year, water scarcity values were high in mostly alfalfa areas, whereas cotton areas have mostly no stress with good water availability. The major water users of crops, ranked in order, were alfalfa, pecans, cotton, and corn. During the dry year, water availability showed to be balanced in terms of water supply and demand by controlling crop patterns from reducing alfalfa acreage by 12% and increasing cotton acreage by 13%.     

Mate choice among sympatric fur seals: female preference for conphenotypic males

When closely related species breed in sympatry, and where hybrids have lower fitness, reinforcement theory predicts that selection should favour mechanisms that reduce the probability of interspecific matings. If this situation arises among species that exhibit resource defence polygyny where males and females of different species reside in the same territories, there may be some conflict between mate choice based on territory-holding ability (sexual selection) and mate choice for correct species. We investigated this in a population of fur seals where three species are sympatric and where some females breed in the territories of heterospecific males, and where interspecific matings and hybrid pups are observed. The territorial status of males and the birthing sites of females were determined during daily observations, as were the movements of males and females, the location of matings and mating partners. DNA extracted from skin samples was used to determine paternities using DNA fingerprinting and the mtDNA genotype of individuals. Individuals were also classed on the basis of species-typical phenotype. We found that extra-territory inseminations (ETIs) were significantly more prevalent (67%) when territorial males and resident females were of different phenotype than when of similar phenotype (27%), but mtDNA genotype had no effect on the rate of ETIs. ETIs were probably by males with the same phenotype, as pups born to these females in the following season had the same phenotype as their mothers, suggesting they were not hybrids. These results suggest that within the resource defence polygynous mating system of these sympatric fur seals, female mate choice is more influenced by male phenotype than genotype. Contrary to our predictions, our study indicates that potential conflict between mate choice based on sexual selection and species recognition is unlikely, because females have some capacity to discriminate between males both within and between species on phenotypic traits additional to those under sexual selection. Although at least 25% of the pups born in this study were hybrid, this study can only support reinforcement theory if hybrids have reduced fitness. The fitness of hybrids among the species studied is currently unknown. Received: 19 January 1998 / Accepted after revision: 12 September 1998     

Effect of Information Availability on Assessment and Designation of Species at Risk

Abstract: Information required to evaluate the extent to which species are at risk of extinction is usually limited and characterized as highly uncertain. In this context, we define information availability as the presence or absence of information used to determine the value of an ecological variable. We examined which of three hypothetical approaches best matched how levels of risk are assigned to species: (1) precautionary approach in which analysts designate levels of risk regardless of the amount of information available, (2) worst‐case approach in which analysts assign the maximum level of risk possible from the criteria, and (3) insurance approach in which analysts assign poorly known species to a high‐risk category when little information is available. We used the quantitative assessment criteria of the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) as a case study. We created a binary (0/1) matrix of all 2.4192 × 10⁷ logical combinations of available information for the 14 ecological variables included in the quantitative criteria. We processed each combination of information availability represented in the matrix with a computer algorithm designed to emulate COSEWIC decision‐making rules. Low information availability was associated with a relatively high frequency of not being able to assign a candidate taxon to a risk category, which does not follow the precautionary principle. Information availability and the level of risk assigned to species were directly related, which is associated with the worst‐case approach, and counter to the insurance approach. Our results suggest that information availability can have a major effect on the level of risk assigned to a species. We recommend a conscious determination of whether such effects are desired, and we recommend the development of methods to explicitly characterize and incorporate information availability and other sources of uncertainty in decision‐making processes.