Biased parental investment and reproductive success in Gabbra pastoralists

Demographic data from 848 Gabbra households are used to examine the relationships between herd size and reproductive success in relation to sex, in a traditional, pastoralist population. The number of camels in the household herd has a significant positive effect on the reproductive success of both men and women, although the effect of wealth is greater for men, as predicted from evolutionary theory. The greater the number of elder brothers a man has, the lower his reproductive success, as a result of a smaller initial herd and a later age at marriage. This is not true for women –number of elder sisters does not have a measurable effect on a woman’s fertility, although it does have a small, negative effect on the size of her dowry. These results are interpreted as competition between same-sex siblings for parental investment, in the form of their father’s herd, which is more intense between sons than daughters as parental investments are greatest in males. Received: 30 June 1995/Accepted after revision: 23 October 1995     

Paternity and condition affect cannibalistic behavior in nest-tending bluegill sunfish

Theory of parental care evolution predicts that a parent should invest more in a brood when its fitness value is greater than alternative investments such as the parent's own survivorship or future broods. In fish, filial cannibalism (eating one's own offspring) is widespread and represents a challenge to parental care evolution. In this study, I investigated filial cannibalism in bluegill sunfish (Lepomis macrochirus). Bluegill are characterized by alternative mating tactics referred to as "parentals" and "cuckolders". Parentals delay maturation, construct nests, court females and provide sole parental care for the developing offspring. Cuckolders mature precociously and parasitize parentals using two tactics called "sneakers" and "satellites". I found that parentals that obtained fewer eggs during spawning appeared more likely to completely cannibalize their brood (total filial cannibalism: P=0.07), regardless of their condition. Among parentals that provided care, partial cannibalism was greater during the egg phase as compared to the fry phase of care, but it was unrelated to brood size. Throughout the care period, parentals in better condition were less likely to partially cannibalize their brood, indicating that parentals use cannibalism to replenish energy reserves. Independent of condition, parentals that were cuckolded more were more likely to eat part of their brood. This relationship was evident only after the eggs had hatched, which is consistent with data showing that parentals can use olfactory cues produced by fry but not eggs to assess their paternity. This latter result proposes that parentals may be selectively culling cuckolder offspring from their nest. These data provide empirical support for parental care theory, and the first evidence for the importance of paternity on cannibalistic behavior.Communicated by M. Abrahams     

Testosterone and helping behavior in the azure-winged magpie (Cyanopica cyanus): natural covariation and an experimental test

In this study, we investigated patterns of natural covariation between testosterone and reproductive status in a cooperatively breeding bird species, the azure-winged magpie (Cyanopica cyanus). To assess the relationship between testosterone and breeding behavior, we also manipulated testosterone (T) levels early in the season (before breeding started) using testosterone-filled or empty implants. Our results do not support the hypothesis that circulating testosterone levels affect the occurrence of helping behavior in the azure-winged magpie. Helping males had similar T levels to breeding males. Furthermore, experimentally augmented plasma T did not affect the likelihood of becoming either a helper or a breeder. Overall, these results are consistent with previous findings in other bird species and only give some support to the behavioral suppression hypothesis, suggesting that helping in the azure-winged magpie is a flexible behavioral option moderated in the short-term by social and ecological factors. Experimentally elevated testosterone levels, however, reduced the reproductive success of male breeders because of markedly lower levels of paternal care, had similar effects on their mates, but had the contrary effect on helpers, which raised levels of parental effort. We suggest increases in the share of paternity and in social prestige as possible explanations for these results.Communicated by: A. Cockburn     

A predator’s preference for egg-carrying prey: a novel cost of parental care

Using a subsocial spitting spider (Scytodes pallida) as the prey and a spider-eating jumping spider (Portia labiata) as the predator, the cost of parental care is investigated. Our findings suggest that being singled out as preferred prey by P. labiata is, for egg-carrying females of S. pallida, an important cost of parental care. In survival tests, during which P. labiata was given access to egg-carrying and eggless S. pallida females, egg-carrying females were preyed on more often than eggless females. In preference tests, motionless lures instead of living S. pallida were used. The lures were made by mounting dead egg-carrying and dead eggless S. pallida females in lifelike posture in webs. In these tests, P. labiata detected and identified, by vision alone, both kinds of prey (egg-carrying and eggless), and singled out egg-carrying females as preferred prey.Communicated by M.A. Elgar     

Adjustment of parental effort in the puffin; the roles of adult body condition and chick size

 We examined the adjustment of parental effort of puffins by switching 20-day-old chicks randomly between parents of known body condition. Among unmanipulated birds mass gain (5–20 days) and mass of 20-day-old chicks was positively correlated with the body condition of parents at day 6. During the first 5 days after chick switching 28% (n = 55) of the parents deserted their foster chick. Parents which deserted their foster chick originally had a chick of their own that was smaller than that of those which did not desert their foster chick. Whether parents deserted their foster chick was also negatively related to the size of the foster chick. The mass of the foster chick was more important than the size of the parents' own chick in determining the desertion rate of chicks. The mass gain of the foster chick during the first 5 days after switching was positively related to the body condition of foster parents and also positively related to the mass of the foster parents' own chick, but negatively related to the size of the foster chick. The results suggest that puffins adjust their parental effort according to both their own body condition and the size of the chick. The latter may indicate the chick's prospect of survival and recruitment to the population. Received: 20 January 1996 / Accepted after revision: 27 October 1996     

海河流域不同植物砣含量、地域分异及其输入、输出量研究

海河流域是我国农业发展的一个重要基地,由于不合理开发利用,造成某些地区土壤出现贫瘠化、盐渍化和沙漠化,土壤缺磷也很明显.为了寻找植物对磷的需求特点以及海河流域土壤磷分布规律,可以从植物指示的角度研究不同地区不同植物磷含量特征及其差异,研究植物每年从土壤中输出和输入的磷总量,从而寻找农业生态系统磷循环规律并科学指导施肥.     

AN AUTO-CAD-BASED WATERSHED INFORMATION SYSTEM FOR THE HYDROLOGIC MODEL HEC-11

ABSTRACT: A micro computer based Watershed Information System (W.LS.) is developed to assist in the preparation of input files for the hydrologic simulation model HEC-1. This system consists of three phases. Phase I utilizes the capabilities of AutoCAD version 9 and three programs, BASINS, PLANES, and CHANNELS, to extract, organize, and display watershed data. Phase II uses the program CN to calculate some HEC-1 parameter values. Phase II utilizes the program HECUPDATE to create HEC-1 input files. The system input includes topographic, soils, land use, watershed geometry data, and a skeletal HEC-1 input file. Output from the system includes a summary User Reference File, a Soils File, a Land Use File, a Watershed Geometry File, a Curve Number File, and a HEC-1 input file, which is ready to run. The W.I.S. has been applied to Macks Creek Watershed in southwest Idaho.     

Defending young biparentally: female risk-taking with and without a male in the burying beetle, <Emphasis Type="Italic">Nicrophorus pustulatus</Emphasis>

A positive correlation between the parental effort of a male and female should promote stable biparental care. Risk-taking (as assessed by injuries) against infanticidal intruders by Nicrophorus pustulatus females was expected to be low when females had a low probability of successful defense of the young. I tested the hypothesis that when the presence of a male partner increased the probability of successful defense from low to moderate that female risk-taking would increase. Single females and pairs with first instar larvae were confronted by potentially infanticidal male and female conspecific intruders. Male intruders routinely took over nests from unpaired females (30 of 36 trials). Unpaired females and male intruders were injured infrequently, indicating less intense fights despite the high probability of infanticide. A resident female defending against a male intruder was injured more often when paired than unpaired, suggesting greater risk-taking. A male parent that delays desertion, therefore, receives fitness benefits not only from his own defense of the young, but from greater female defense against male intruders as well. It is hypothesized that the threat of infanticidal takeovers by males promotes extended biparental care in burying beetles. When the intruder was female, on the other hand, a female parent on her own had a moderate probability of successfully defending the brood (22 of 36 trials). The presence of a male partner against female intruders almost guaranteed successful defense (35 of 36 trials) and female intruders did not appear to contest pairs vigorously. Against female intruders the presence of a male partner did not significantly change injury rates of the defending female.     

Sex-specific maternal effect on egg mass,laying order,and sibling competition in the Bengalese finch (<Emphasis Type="Italic">Lonchura striata</Emphasis> var. <Emphasis Type="Italic">domestica</Emphasis>)

Maternal effects, such as investment in eggs, have profound effects on offspring fitness. Mothers are expected to skew their investment depending on the laying order and sex when unequal sibling competition occurs within a brood because of sex-specific vulnerability and age hierarchy caused by asynchronous hatching. The Bengalese finch hatches asynchronously and shows a moderate reversed sexual size dimorphism. However, contrary to commonly accepted assumptions of size-dependent vulnerability, the smaller sex (male) is more vulnerable to developmental stress caused by sibling competition. We investigated whether maternal investment would be biased by the position in laying order and the sex of eggs, and also explored the possible differences in growth patterns depending on sex, laying order, and age hierarchy by observing chicks fostered to experimentally manipulated broods where brood composition was controlled and age hierarchy was more enhanced than in natural breeding conditions. We found that overall patterns of maternal investment favored the disadvantageous sectors of sibling competition, i.e., eggs of later laying order and sons over those of early laying order and daughters. We also examined the effect of laying order on adult body size and sex differences in growth patterns. When reared in the subordinate age hierarchy, females could compensate for the deficit of decreased growth rate by taking longer to mature, whereas males could not. We suggest that this sex-specific growth pattern could be the cause of sex differences in vulnerability to early developmental stress.     

Male care of infants in a siamang (Symphalangus syndactylus) population including socially monogamous and polyandrous groups

While male parental care is uncommon in mammals, siamang (Symphalangus syndactylus) males provide care for infants in the form of infant carrying. I collected behavioral data from a cohort of five wild siamang infants from early infancy until age 15–24 months to identify factors affecting male care and to assess the consequences of male care for males, females, and infants in a population including socially monogamous groups and polyandrous groups. There was substantial variation in male caring behavior. All males in polyandrous groups provided care for infants, but males in socially monogamous groups provided substantially more care than males in polyandrous groups, even when the combined effort of all males in a group was considered. These results suggest that polyandry in siamangs is unlikely to be promoted by the need for “helpers.” Infants receiving more care from males did not receive more care overall because females compensated for increases in male care by reducing their own caring effort. There was no significant relationship between indicators of male–female social bond strength and male time spent carrying infants, and the onset of male care was not associated with a change in copulation rates. Females providing more care for infants had significantly longer interbirth intervals. Male care may reduce the energetic costs of reproduction for females, permitting higher female reproductive rates.