The influence of body size on immediate reproductive success in Dugesia gonocephala (Tricladida,Paludicola)

The individual reproductive output of the stream-dwelling flatworm Dugesia gonocephala was investigated. Various measures of reproductive success were related to body size. (I) For the first 30 days in the laboratory small individuals produced no cocoons, individuals of intermediate size produced unfertilized cocoons and large individuals usually produced fertilized cocoons. (II) In individuals that produced a cocoon, no correlation was found between the number of cocoons produced in one month and body size. (III) Large individuals, however, produced larger cocoons. This was not due to the fact that unfertilized cocoons were smaller. (IV) Large cocoons tended to contain more young. (V) The average size of young hatching from large cocoons was larger. (VI) Large individuals produced their first cocoon soon after their arrival in the laboratory and seemed to have a higher chance of producing a fertilized first cocoon. (VII) A trade-off existed between producing many small versus few large young.     

Plant size,breeding system,and limits to reproductive success in two sister species of Ferocactus (Cactaceae)

Plant reproductive output can be limited by a variety of factors, bothintrinsic and extrinsic. I investigated the reproductive biologies of twospecies of unbranched short-columnar cacti, Ferocactuscylindraceus and F. wislizeni. I recordedfemalereproductive output (flowers produced, fruit set, seeds per fruit and seedmass), plant size and growth, and used hand-pollination experiments todeterminebreeding systems and pollen limitation. In both species, the ability to selfvaried among individuals, but self-pollination resulted in very few seeds,suggesting strong inbreeding depression. Neither species was pollen-limited.Numbers of flowers produced increases with plant size for both species, andseeds per fruit may also be related to plant size, although the relationship isunclear. Seed mass is not correlated with plant size. Flower production wassimilar in both species, but F. cylindraceus producedfewerseeds per fruit than F. wislizeni, and its seeds weighedless. Fruit set by F. cylindraceus was heavily impacted bya florivorous lepidopteran. Fruit set was very high (94 to 96%) inF. wislizeni, suggesting that architectural constraints(e.g., meristem limitation) are more limiting than resource levels or the levelof pollinator services. In F. cylindraceus, numbers ofseeds per fruit was positively correlated with seed mass, whereas inF. wislizeni, the relationship was negative (tradeoff).Thegrowth rates of F. wislizeni are affected by rainfall theprevious season, and growth rates increase as the plant ages.Ferocactus cylindraceus and F.wislizeni are thought to be sister species, meaning that observeddifferences between them are more likely to be the result of recentevolutionaryprocesses in their lineages rather than differing phylogenetic histories.     

Selection for fertility in mice using different methods of litter size manipulation

Summary A short-term selection experiment for increasing the first-day litter size (LS1) and 28-day litter weight (LW28) was conducted with three populations of mice over 8 generations. Different methods of litter size manipulation were used for the populations — in S the litter size was standardized to 8 (4 , 4 ) on the first day, in LA it was adjusted to the average size of all litters born on the same day and NL had the natural litter size. To eliminate temporary environmental effects, a control population was kept in each case. The selection results per generation were, for LS 1 b=0.30 (S, NL) and 0.20 (LA), and for LW28 b=5.62 g (S), 5.26 g (NL), and 4.32 g (LA). The heritability obtained was between 0.18 and 0.13 for LS 1 and from 0.42 to 0.12 for LW28. The populations differed in the correlated responses for body weight parameters (litter weight gain). The implantation rate increased in populations S and NL (b=0.19, 0.37), but not in population LA. Postnatal mortality went down (b=-0.07) and the dam's milk production rose (b=1.11 g) only in population LA. The estimated partial regression coefficient linking body weight at mating (BWM) for the dam and the daughter's litter size showed an effect on the litter size.     

Experimental manipulation of breeding density and litter size: effects on reproductive success in the bank vole

1. Reproductive success of individual females may be determined by density-dependent effects, especially in species where territory provides the resources for a reproducing female and territory size is inversely density-dependent.
2. We manipulated simultaneously the reproductive effort (litter size manipulation: ± 0 and + 2 pups) and breeding density (low and high) of nursing female bank voles Clethrionomys glareolus in outdoor enclosures. We studied whether the reproductive success (number and quality of offspring) of individual females is density-dependent, and whether females can compensate for increased reproductive effort when not limited by saturated breeding density.
3. The females nursing their young in the low density weaned significantly more offspring than females in the high density, independent of litter manipulation.
4. Litter enlargements did not increase the number of weanlings per female, but offspring from enlarged litters had lower weight than control litters.
5. In the reduced density females increased the size of their home range, but litter manipulation had no significant effect on spacing behaviour of females. Increased home range size did not result in heavier weanlings.
6. Mother's failure to successfully wean any offspring was more common in the high density treatment, whereas litter manipulation or mother's weight did not affect weaning success.
7. We conclude that reproductive success of bank vole females is negatively density-dependent in terms of number, but not in the quality of weanlings.
8. The nursing effort of females (i.e. the ability to provide enough food for pups) seems not to be limited by density-dependent factors.     

Effects of clutch size manipulations on reproductive behaviour and nesting success in the cooperatively breeding Bell Miner (Manorina melanophrys)

Summary An experimental manipulation of clutch size was carried out on a wild population of the cooperatively breeding Bell Miner (Manorina melanophrys, Meliphagidae) to assess which factor(s) limit clutch size in this species. Results provide some support for the trade-off hypothesis since there is a cost of reproduction for the breeding female in terms of loss of body mass. The breeding female performs most of the nestling care. Clutches of three eggs are also laid during the mid-breeding season which is the period most favourable for breeding (i.e. nestlings grow faster). This evidence also supports the intrabrood competition hypothesis. Clutches that have lost an egg were more likely to be deserted; this may be an antipredator strategy since partial clutch predation has been recorded in the field. Nest predation was high in this study (64.9%), suggesting that many small clutches may be a strategy to decrease the effect of nest predation on reproductive success over the whole breeding season (nest predation hypothesis). Both the trade-off hypothesis and the nest predation hypothesis may apply in this case since they are not mutually exclusive. The size of the attending group did not greatly affect reproductive success in the short term, although if both age structure and size of the group are taken into account, reproductive success can be better predicted.     

Offspring growth, survival and reproductive success in the bank vole: a litter size manipulation experiment

To estimate the optimality of brood size, it is essential to study the effects of brood size manipulation on offspring survival and reproductive success. Moreover, testing the generality of the hypothesis of reproductive costs requires experimental data from a diversity of organisms. Here I present data on the growth, survival and reproductive success of bank vole Clethrionomys glareolus individuals from manipulated litters. Furthermore, the survival of mothers whose litter size was manipulated was studied. At weaning, the mean weight of pups from enlarged litters was lower and from reduced litters higher compared to control litters. After winter, at the start of the breeding season, individuals from enlarged litters, especially males, were still lighter than individuals from the other two treatments. Litter enlargements did not increase the number of reproducing female offspring per mother, nor did the litter sizes of female offspring differ between treatments. There were no differences between treatments in winter survival of offspring after weaning, but among female offspring, weaning weight explained the survival probabilities over winter. A higher weight of females at winter determined the probability of starting to reproduce in spring. The survival of mothers did not seem to be influenced by litter manipulation performed the previous year. According to the results, mothers nursing enlarged or reduced litters do not gain any fitness benefits in terms of number of offspring surviving to breeding. The results are consistent with the majority of experiments conducted in birds, which have found costs of enlarged brood appearing as offspring trade-offs rather than parent trade-offs. Received: 14 December 1997 / Accepted: 1 March 1998     

Experimentally induced clutch size enlargements affect reproductive success in the Pied Flycatcher

We performed a food provisioning experiment in a population of Pied Flycatchers Ficedula hypoleuca breeding at high altitude in central Spain to test if food availability before and during laying determines clutch size. Food was provided to one of two pairs with the same date of initiation of nest-building (15 dyads of subsequently reproducing pairs were thus created). Food provisioning began on the day of initiation of nest-building and ended on the day after the last egg was laid. Although laying date was unaffected by the experiment, clutch size in the experimental treatment was significantly larger. This result could indicate that food availability at laying (1) proximately constrained clutch size or (2) that females evaluated future conditions for incubating eggs and feeding nestlings based on food availability at laying. Reproductive success (proportion of eggs that resulted in fledged young) was significantly reduced in the experimental treatment. This effect suggest that supplemented females were tricked by the experiment into laying more eggs than the number of eggs they were able to incubate with success and the number of nestlings they were able to feed, a source of error in clutch size adjustment which could be common in non-experimental situations.     

Photosynthesis in relation to reproductive success of Cypripedium flavum

* BACKGROUND AND AIMS: Cypripedium flavum is a rare, endemic alpine slipper orchid of China, which is under threat from excessive collection and habitat changes. Conservation and re-introduction of C. flavum is restricted by lack of knowledge of the plant's photosynthesis and how that affects reproductive success. The hypothesis is tested that reproductive success is determined by photosynthetic production. * METHODS: To understand the photosynthetic characteristics and adaptation of C. flavum to alpine environments, and the relation to reproductive success, measurements were made at four field sites with varying degrees of forest cover in the Hengduan Mountains, south-west China. * KEY RESULTS: Both photosynthetic capacity and reproductive traits of C. flavum are affected by light availability. Photosynthetic rate (A) is greatest around noon, following the pattern of photosynthetically active radiation (PAR) at all sites. Cypripedium flavum has highest daily mean photosynthetic rate (A(daily)) and light-saturated photosynthetic rate (A(max)) under a half to a third of full sunlight. High radiation decreased A. However, the optimum temperature for photosynthesis was similar (18-20 degrees C) at all sites. * CONCLUSIONS: The quotient of daily mean photosynthetic rate to light saturated photosynthesis (A(daily)/A(max)) is positively correlated with the ramet number m(-2) and percentage of fruiting of C. flavum. The A(daily)/A(max) ratio is a useful proxy for evaluating reproductive success of C. flavum.     

The effects of dominance rank and group size on female lifetime reproductive success in wild long-tailed macaques,Macaca fascicularis

Demographic changes were recorded throughout a 12-year period for three social groups ofMacaca fascicularis in a natural population at Ketambe (Sumatra, Indonesia). We examined the prediction that females' lifetime reproductive success depended on dominance rank and group size. Average birth rate was 0.53 (184 infants born during 349 female years). For mature females (aged 8–20 yr) birth rate reflected physical condition, being higher in years with high food availability and lower in the year following the production of a surviving infant. High-ranking females were significantly more likely than low-ranking ones to give birth again when they did have a surviving offspring born the year before (0.50 vs 0.26), especially in years with relatively low food availability (0.37 vs 0.10). Controlled comparisons of groups at different sizes indicate a decline in birth rate with rroup size only once a group has exceeded a certain size. The dominance effect on birth rate tended to be strongest in large groups. Survival of infants was rank-dependent, but the survival of juveniles was not. There was a trend for offspring survival to be lower in large groups than in mid-sized or small groups. However, rank and group size interacted, in that rank effects on offspring survival were strongest in large groups. High-ranking females were less likely to die themselves during their top-reproductive years, and thus on average had longer reproductive careers. We estimated female lifetime reproductive success based on calculated age-specific birth rates and survival rates. The effects of rank and group size (contest and scramble) on birth rate, offspring survival, age of first reproduction for daughters, and length of reproductive career, while not each consistently statistically significant, added up to substantial effects on estimated lifetime reproductive success. The group size effects explain why large groups tend to split permanently. Since females are philopatric in this species, and daughters achieve dominance rank positions similar to their mother, a close correlation is suggested between the lifetime reproductive success of mothers and daughters. For sons, too, maternal dominance affected their reproductive success: high-born males were more likely to become top-dominant (in another group). These data support the idea that natural selection has favored the evolution of a nepotistic rank system in this species, even if the annual benefits of dominance are small.     

Short- and long-term effects of litter size manipulation in a small wild-derived rodent

Iteroparous organisms maximize their overall fitness by optimizing their reproductive effort over multiple reproductive events. Hence, changes in reproductive effort are expected to have both short- and long-term consequences on parents and their offspring. In laboratory rodents, manipulation of reproductive efforts during lactation has however revealed few short-term reproductive adjustments, suggesting that female laboratory rodents express maximal rather than optimal levels of reproductive investment as observed in semelparous organisms. Using a litter size manipulation (LSM) experiment in a small wild-derived rodent (the common vole; Microtus arvalis), we show that females altered their reproductive efforts in response to LSM, with females having higher metabolic rates and showing alternative body mass dynamics when rearing an enlarged rather than reduced litter. Those differences in female reproductive effort were nonetheless insufficient to fully match their pups’ energy demand, pups being lighter at weaning in enlarged litters. Interestingly, female reproductive effort changes had long-term consequences, with females that had previously reared an enlarged litter being lighter at the birth of their subsequent litter and producing lower quality pups. We discuss the significance of using wild-derived animals in studies of reproductive effort optimization.     

Meadow voles and prairie voles differ in the percentage of conspecific marks they over-mark

Many terrestrial mammals scent mark in areas containing the scent marks of conspecifics, and thus, may deposit their own scent marks on top of those that were deposited previously by conspecifics. This phenomenon, known as over-marking appears to play a role in same-sex competition or mate attraction. The present study determines whether meadow and prairie voles avoid over-marking the scent marks of conspecifics, target the scent marks of conspecifics and over-mark them, or randomly over-mark the scent marks of conspecifics. The data show that meadow and prairie voles adjust the number and location of scent marks that they deposit in areas marked previously by particular conspecifics. Male and female meadow and prairie voles target the scent marks of opposite-sex conspecifics and over-mark them. Female meadow and prairie voles also target the scent marks of female conspecifics. In contrast, male meadow and prairie voles over-mark the scent marks of male conspecifics in a random manner. By differentially over-marking the scent marks of conspecifics, voles may be able to communicate particular information to a variety of conspecifics.     

The effects of male body size on territorial and mating success in the landmark-defending fly Hermetia comstocki (Stratiomyidae)

Abstract.

• 1 Males of Hermetia comstocki Williston compete for territorial control of certain agaves and yuccas. Winners copulate with females that visit these plants solely to acquire a mate.
• 2 Males vary in body weight by more than an order of magnitude and larger flies almost always defeat smaller ones in aerial contests for control of landmark territories.
• 3 The mean body size (as measured by wing-length) was significantly greater for males retaining residency at a site for at least one hour compared to males unable to do so. Likewise, males able to return to a perch site in the study area on more than one day were larger on average than males unable to do so.
• 4 Male preferences for landmark territories remained similar across years. Large males dominated the perch landmarks most likely to be occupied by males and most likely to be visited by females.
• 5 Despite the fighting and territorial advantages enjoyed by large males, the mean size of males found mating with females was not significantly larger than that of the general population.
• 6 The apparent failure of large males to secure a statistically significant mating advantage may be a statistical consequence of the small sample size of males observed mating. On the other hand, any mating advantage of large males may be reduced because (a) receptive females visit many different landmarks, (b) females mate with the first male they encounter at a landmark, regardless of his size, (c) there are usually many vacant landmarks available for smaller males, and (d) even popular territories are often open to small males, thanks to the low site-tenacity of territory owners.

     

Effects of superabundant food on breeding success and behavior of the red-winged blackbird

Summary The effects of food on breeding success and behavior of the red-winged blackbird (Icteridae: Agelaius phoeniceus) were investigated during 3 successive breeding seasons. In the second season, a 4-week pulse of abundant food in the form of a periodical cicada emergence (Homoptera: Cicadidae: Magicicada spp.) occurred in the forest adjacent to the marsh where the birds were breeding.During the cicada period, the bird population showed: 1) an increase in foraging trips to the forest and a decrease in trips per h, 2) increased biomass of nestlings, 3) increased nestling survival caused by decreased starvation, 4) increased fledging success, and 5) bimodal weight distributions of older nestlings (reflective of the sexual dimorphism in this species). These data suggest the temporary removal of food limitations on the breeding population when the pulse of food was available.