Assessing the effect of radiocollars on juvenile guanaco survival

To evaluate the potential impact of our research activities on guanacos (Lama guanicoe), we tested for effects of radiocollaring on juvenile (≤1 year of age) survival in Torres del Paine National Park, Chile during 1992–1996. The survival of collared (40.1%) and uncollared (38.2%) juveniles was not significantly different (G=0.08; P=0.77). Our results suggest that radiocollaring does not adversely affect the survival of juvenile guanacos. Although we observed no effect of radiocollaring, we still underline the importance of testing for effects of radiocollars in other wildlife investigations when feasible. Received: 20 September 1999 / Accepted: 8 March 2000     

Selfish mothers: reproductive expenditure and resource availability in bighorn ewes

We present a marginal value model explaining intraspecific andinterspecific variation of mating systems in nonterritorialungulates. The model takes into account the simultaneous effectsof spatial and temporal distribution of females, female groupsize, male-male competition, female choice, and the operationalsex ratio (i.e., the proportion of estrous females). The modelpredicts that higher numbers of females per group increasesthe average exploitation time of such groups by males. An increasein female group density, operational sex ratio, and age-specificfighting success of males are predicted to reduce the averageexploitation time of female groups, leading to roving of males(i.e., moving between female groups). In contrast, an increasein die female rejection rate of males and in the time spentby males on nonmating activities (i. e., foraging, lying down,ruminating, migrating) are predicted to increase the averageexploitation time of female groups and to favor staying behaviorof males (i.e., defending a female group over a longer periodof time). Consequently, die model predicts that young maleswill tend to be "stayers," whereas middle-aged and old malesare expected to be "rovers." Model predictions were tested widifield data collected on muskoxen Ovibos moschatus in a naturalpopulation in west Greenland. Observed correlations betweenbull exploitation times of cow groups and the six above-mentionedsocial and environmental parameters were all in die predicteddirection and statistically significant in five of die six cases.Overall, 69% of die observed variation in exploitation timeof cow groups by males was explained by die model predictions.Stepwise regression suggested that, of die six parameters, variationin sex ratio (R² = .56) and time spent on nonmating activities(R² = .35) had the largest effects on male exploitation time.Also, die observed age-specific variation in bull exploitationtime of cow groups was as predicted.     

An experimental analysis of mate choice in the wren: a monomorphic, polygynous passerine

Male wrens (Troglodytes troglodytes) construct nests that areused in their display to females. Previous work has suggestedthat the number of vacant nests may be used as a mate choicecue. Correlational data from 1992 confirmed that females appearedto be assessing die number of vacant nests on a male's territoryand preferentially mating with males with more nests. Male taillengdi was also correlated widi mating success. In 1993 thenumbers of nests on territories was experimentally manipulated,the female setdement patterns confirmed that die number of vacantnests did mediate mate choice. Male tail length failed to explainadditional variance in mating success when die variance explainedby the experimental manipulation was removed, suggesting diatdie original correlation arose because both tail length andmating success were correlated widi a confounding variable.The structure of the vegetation in a male's territory influencedmating success. This appeared to be due to nests surviving betterin territories widi dense vegetation. Males on territories inwhich nests survive well had longer tails. Male-male competitionfor good territories may explain die observed effects of malemorphology on mating success. Furdier analysis of die nest choicedata showed diat all nests had an equal chance of being usedby a female. The fact diat all nests had an equal probabilityof being chosen by a female means diat each additional nestbuilt by a male wren results in die same increase in matingsuccess. This suggests diat die benefits to males of nest buildingincrease linearly. The number of nests on a territory will beaffected by various factors such as predation pressure, nestbuilding rate, and vegetation structure. The information diatfemales are getting by assessing such a signal is discussed.     

Early development, adult mass, and reproductive success in bighorn sheep

Despite considerable empirical and theoretical work on the individualand population consequences of early development, little isknown about the correlations between early mass and adult sizeor lifetime reproductive success of free-ranging mammals. Usinga 26-year study of bighorn sheep (Ovis canadensis), we examinedhow mass as a lamb and mass gain as a yearling affected adultmass for both sexes, horn length of males and lifetime reproductivesuccess of females at different population densities. Mass asa 3-week-old lamb was either weakly or not correlated withadult mass, horn length of adult males, or the number of lambsweaned over a ewe's lifetime. Weaning mass was correlated withmost of these variables when the number of ewes in the populationwas taken into account. When weaning mass was controlled throughpartial correlation, mass as a yearling was correlated with adult mass of ewes but not with ewe reproductive success orwith adult mass or horn length of rams. Lamb mass and numberof ewes explained more of the variance in adult characteristicsfor males than for females. Our results suggest that mass gainduring lactation, possibly but not necessarily related to theamount of maternal care received, affects adult mass and reproductive success. Females appear better able than males to compensatefor poor early development, likely by postponing their firstreproduction. Mass gain over several years and the number ofewes in the population strongly affect adult mass of both sexesand therefore can have profound effects on reproductive successof this long-lived species with a multi-year growth period.     

Maternal influence on the incidence and duration of larval diapause in Calliphora vicina

ABSTRACT. The photoperiodic mechanism governing larval diapause in the blowfly Calliphora vicina R.-D. (Diptera: Calliphoridac) is largely maternal. The critical daylength for adult flies at 20C, and larvae derived from day 12 eggs and maintained in darkness at 11C, is about 14.5 h/24. At short daylength (LD 12:12 h) and a range of temperatures, eggs laid on or before day 9 gave rise to a low incidence of diapause, whereas those laid on day 10 and later gave rise to a high incidence; the photoperiodic 'counter' therefore shows a temperature-compensated mechanism for 'accumulating' successive short days. The rate of switching from non-diapause to diapause progeny is hardly affected by the timing of protein meals, although an early supply of meat accelerates egg development and leads to an increasing proportion of early, non-diapausing progeny. There is no evidence for a maternal effect preventing diapause induction in the first post-diapause ('spring') generation of flies. Diapausing larvae terminate diapause spontaneously in darkness at 11C after a variable period which is positively correlated with the incidence of diapause in the group. Diapause incidence and duration therefore are both determined maternally.     

Energy expenditure, nestling age, and brood size: an experimental study of parental behavior in the great tit Parus major

A brood manipulation experiment on great tits Parus major was performedto study the effects of nestling age and brood size on parentalcare and offspring survival. Daily energy expenditure (DEE)of females feeding nestlings of 6 and 12 days of age was measuredusing the doubly-labeled water technique. Females adjusted theirbrooding behavior to the age of the young. The data are consistentwith the idea that brooding behavior was determined primarilyby the thermoregulatory requirements of the brood. Female DEEdid not differ with nestling age; when differences in body masswere controlled for, it was lower during the brooding periodthan later. In enlarged broods, both parents showed significantlyhigher rates of food provisioning to the brood. Female DEE wasaffected by brood size manipulation, and it did not level offwith brood size. There was no significant effect of nestlingage on the relation between DEE and manipulation. Birds wereable to raise a larger brood than the natural brood size, althoughlarger broods suffered from increased nestling mortality ratesduring the peak demand period of the nestlings. Offspring conditionat fledging was negatively affected by brood size manipulation,but recruitment rate per brood was positively related to broodsize, suggesting that the optimal brood size exceeds the naturalbrood size in this population.     

Birth weight variation in the domestic pig: effects on offspring survival, weight gain and suckling behaviour

In domestic pigs, litter-mates often vary considerably in birth weight. To examine whether this size variation influences piglet survival, weight gain and suckling behaviour, we experimentally manipulated the number and size distribution of litter-mates in 51 litters. Litters were small (eight or nine piglets) or large (11 or 12 piglets) compared to the herd mean of 10 piglets, and were made more or less variable in weight by using the largest and smallest quartiles of two combined litters (variable) or the middle two quartiles (uniform). Weights were measured on days 0, 3 and 21. Behavioural measures (percent of nursings missed, mean teat consistency score, per capita number of teat disputes before milk ejection, and percent time spent in teat disputes in the 20min after milk ejection) were recorded on days 1, 4, 10 and 17. Piglet weight variation (percent of coefficient of variation, CV) almost doubled over the 21 days in uniform litters and actually decreased in variable litters, but still remained higher in the variable litters. Overall, survival, percent of nursings missed, consistency in piglets' use of teats, number of teat disputes, percent time a piglet spent in teat disputes after milk ejection, and weight gain were unaffected by birth weight variation although there was a tendency (P=0.09) for more piglet deaths in variable litters. Behavioural measures of sibling competition were higher in large litters. The data provide little support for the hypotheses that high birth weight variation results in decreased survival, or that it permits rapid establishment of dominance, thereby reducing wasteful competitive behaviour in surviving piglets.     

Effects of reduced suckling on days to estrus, conception during lactation and embryo survival in sows

Trials to investigate the effects of limited suckling on sow reproduction and piglet growth were conducted using 41 first parity and 32 second parity Yorkshire sows. Separation of sows from their litters (22 hrs/day, days 21-35 postpartum) induced estrus in 60% of primiparous and 72% of second parity sows during lactation. Compared to control group animals, primiparous sows had higher weaning weights and second parity sows higher rates of embryo survival on day 30 of gestation. Piglets subjected to suckling restriction had weights, at 2 weeks after weaning, equal to those weaned after 5 weeks of unrestricted suckling. We conclude that suckling restriction can provide the dual benefits of an extended piglet nursing period and a decreased breeding to breeding interval in sows.     

Fathers, fat, and maternal energetics in a biparental hamster: paternal presence determines the outcome of a current reproductive effort and adipose tissue limits subsequent reproductive effort

Djungarian hamster females, Phodopus campbelli, are severely constrained in their ability to reproduce successfully and lose 20% of their body weight by the time pups are weaned. In the wild and in the laboratory, biparental care improves maternal reproductive success. Two experiments quantified the effects of paternal presence and partial lipectomy [surgical depletion of parametrial white adipose tissue (PWAT) on day 8 of the 18-day gestation] on maternal energy balance, reproductive success, and investment in a subsequent reproductive attempt. Paired females reproduced successfully, maintained body weight, and invested in a second litter. Removal of the male decreased pup survival, growth, and readiness for dispersal by 18 days of age. Solitary females lost 10% of their body weight by the birth and a further 10% by day 18 after the birth. Thus, paternal presence balanced maternal energy budgets during reproduction and prevented a 20% loss in body weight. Equivalent weight loss occurs in response to other maternal stressors, therefore 20% may be the maximum tolerable weight loss in this species. Fresh weight of interscapular brown adipose tissue was predicted by the extent of maternal hyperthermia but not by maternal energy balance or lipectomy. Partial lipectomy did not adversely affect the female or the first litter but decreased the probability of investment in a second reproductive attempt and halved the size of the second litter. This effect may have been due to the 0.1% of body weight amount of lipid removed or may reflect a specialized role for PWAT in adjusting maternal investment.     

Maternal influence on diapause induction in Trichogramma (Hymenoptera: Trichogrammatidae): the dynamics of photosensitivity

It is known that the prepupal diapause in Trichogramma is dependent on temperature conditions of embryonic and larval development and on the photoperiodic conditions of preimaginal development of maternal females. However, the relative photosensitivity of different preimaginal stages has been never investigated. We studied the position of the photosensitive period over the preimaginal development of maternal females in T. embryophagum Htg. and T. principium Sug. et Sor. by transferring preimaginal stages between diapause‐averting ‘long’ day (L : D = 20 : 4) and diapause‐inducing ‘short’ day (L : D = 12 : 12). Results showed that the influence of maternal photoperiod on progeny diapause was determined during the late pupal stage (last days of preimaginal development at 20°C). During this time, the critical duration of the photoperiodic induction was extremely small: one short or long day caused almost the same effect as the permanent development under these conditions. As a whole, photoperiodic response in Trichogramma was found to be unusually rapid, labile and easily reversible which is probably explained by extremely small size and fast development of these egg parasitoids. The results of this study could be used for elaboration of optimal methods for Trichogramma mass rearing and storage and for prediction of its seasonal cycles under natural conditions.     

Environmental effects on prenatal growth rate in pronghorn and bighorn: further evidence for energy constraint on sex-biased maternal expenditure

Byers and Moodie (1990) proposed that high levels of maternalexpenditure in polygynous ungulates limit the ability of mothersto support elevated male fetal and neonatal growth rates. Thishypothesis assumes that females in high-expenditure speciesare at or near the maximum level possible and that females inlower-expenditure species are not. To test this assumption,we examined our long-term data on reproduction of pronghorn(Antilocapra americana) and bighorn (Ovis canadensis) at theNational Bison Range (western Montana, USA) and compared gestationlengths, birth weights, and prenatal growth rates of offspringborn following summers of low versus average or above averageprecipitation. In bighorn, these variables were unaffected bythe previous summer's rainfall, but in pronghorn, gestationlength and prenatal growth rate were significantly lower followingdry summers. Extended samples for both species confirmed earlierreports of sex-biased expenditure favoring males in bighornand the absence of sex-bias in pronghorn. Bighorn prenatal littergrowth rates and birth weights, corrected for maternal mass,are 63.5% and 38%, respectively, of pronghorn values. Thesedata support the Byers and Moodie (1990) contention that femalesof high-expenditure species do not show differential expenditureby offspring sex because they are at a reproductive expendituremaximum, whereas females of lower-expenditure species are ableto support excess expenditure in male offspring because optimalallocation to female offspring is farther from such a maximum.     

Individual, nightly, and seasonal variation in calling behavior of the gray tree frog, Hyla versicolor: implications for energy expenditure

We investigated individual, nightly, and seasonal variationin calling behavior of a population of gray tree frogs (Hylaversicolor) from Connecticut, USA. Repeated recordings of individualmales on seven nights revealed significant differences amongmales in calling rate on all but one night and differences innumber of pulses per call and number of pulses produced perhour (pulse effort) on four nights. Most males reduced callingactivity late at night (after 2230 h), but some maintained arelatively steady rate of call production before dropping outof the chorus. Data collected for 26 individuals recorded onthree or more nights throughout the breeding season revealedsignificant differences among males in calling rate, numberof pulses per call, and pulse effort, but repeatabilities forall three variables were low (0.17, 0.35, and 0.12, respectively).The highest repeatability was for number of pulses per call,a variable strongly influenced by proximity to calling neighbors,probably because males often interacted with neighbors at similardistances on several successive nights. Males tended to reducethe number of pulses per call as the season progressed and thedistance between neighbors decreased, but they showed no clearseasonal change in calling rate or pulse effort. There was asubstantial seasonal decline in the number of hours of chorusactivity, resulting in a median decrease of 43% in nightly energyexpenditure by calling males.     

The influence of eclosion timing on winter survival and triacylglycerol accumulation in four temperate species of Drosophila

Abstract. Diapause incidence, winter survival and triacylglycerol content were studied in temperate species of Drosophila by outdoor rearing in Sapporo (a cool-temperate region), northern Japan. In strains of D.subauraria and D.triauraria (cool-temperate species) from northern Japan, diapause was induced in adults having eclosed after early September, but in those having eclosed after mid October in strains of D.rufa and D.lutescens (warm-temperate species) from southern Japan. A subtropical strain of D.triauraria did not enter diapause. In the strains of cool-temperate species from northern Japan, about 70% survived until spring when eclosed in mid autumn, whereas when eclosed earlier and later flies had a lower ability to overwinter. The warm-temperate species and a subtropical strain of D.triauraria also survived longer when eclosed in mid autumn than when eclosed later, but they were unable to survive until spring. The triacylglycerol content was higher in the cool-temperate species from northern Japan than in the warm-temperate species and a subtropical strain of D.trauraria. In each species the triacylglycerol content of adults was higher when they eclosed in early and mid than in late autumn. It is assumed that triacylglycerol plays an important role in overwintering of these Drosophila species and the low triacylglycerol level is the primary cause of the low overwintering capacity of individuals eclosing in late autumn.     

Genetic and phenotypic variation,dispersal limitation and reproductive success in the invasive herb Eschscholzia californica along an elevation gradient in central Chile

Background: Reductions of genetic diversity and phenotypic changes in invasive plants are often observed to occur at high elevations. Genetic/phenotypic changes of invasive plants along elevation help to understand mechanisms of the presumed resistance of mountain ecosystems to invasion.

Aims: To assess genetic variability and phenotypic plasticity along an elevation gradient of Eschscholzia californica in the Andes, central Chile.

Methods: Eleven microsatellites were used to describe the genetic structure and the allelic diversity individuals, distributed at three elevations and two sites. We assessed the number of flowers per plant, floral biomass, leaf area, number of leaves, vegetative biomass and plant height of plants at each elevation.

Results: Genetic diversity as genetic structure did not decrease with elevations. Plant height and flower numbers decreased while leaf number and vegetative biomass increased with elevation. The ratio of the number of flowers to vegetative biomass, decreased significantly with elevation.

Conclusions: Strong genetic differences among elevations and similar genetic diversity along elevation do not suggest dispersal limitation to higher elevation. Reduction of reproductive and vegetative traits concomitantly with an increase of the reproductive cost suggests reproductive stress with increasing elevation, reducing the invasiveness of this species to higher elevation.     

Genotypic variation for reproductive characters,and the influence of pollen-ovule ratio on selfing rate in rape seed (Brassica napus)

The variance component for genotypic effects and covariable plant vigor were estimated for pollen production, number of ovules, the weight of the flower without anther sacs and pistil, and the gender of the whole plant, in the rape seed variety Topas. There was a significant effect of the genotype for all measured characters. We did not find any trade-off between the male and female functions. Small plants were relatively more male-biased than large plants. The weight of the flower without anther sacs or pistil was positively correlated with pollen production. The selfing rates of the lines were positively correlated with the pollen-ovule ratio, suggesting that the selfing rate of individual plants is positively correlated with pollen-ovule ratio, thus supporting the “mass-action” model. It is proposed that the observed increase in the population selfing rate during the flowering season for some species, including rape seed, can be caused by an overall decrease in male investment.     

Factors affecting offspring survival and development in a cooperative bird: social, maternal and environmental effects

1. In many noncooperative vertebrates, maternal effects commonly influence offspring survival and development. In cooperative vertebrates, where multiple adults help to raise young from a single brood, social effects may reduce or replace maternal effects on offspring. 2. Factors affecting offspring survival and development at different stages (fledging, nutritional independence and adulthood) were tested in the cooperatively breeding Arabian babbler to determine the relative importance of social, maternal and environmental factors at each stage. An influence of maternal effects was found during the nestling stage only. 3. Social factors affected the survival and development of young at all stages. The amount of food received from helpers influenced post-fledging weight gain, development of foraging skills, and survival to reproductive age. Environmental effects were also important, with groups occupying high-quality territories more likely to produce young that survived to maturity. 4. The strong influence of helper contributions on the survival and development of young at all stages from hatching to maturity suggests social factors may have important long-term effects on offspring fitness in cooperative societies. Traditional measures of offspring survival in cooperative birds, which commonly measure survival to fledging age only, may underestimate the significant benefit of helper contributions on the survival and development of young.