Effects of intraspecific competition on size variation and reproductive allocation in a clonal plant

Clonal plants grow in diameter rather than height, and therefore competition among genets is likely to be symmetric and to result in smaller variation in size of genets than in non-clonal plants. Moreover, clonal plants can reproduce both sexually and vegetatively. We studied the effects of density on the size of rosettes and of clones, variation in the size of rosettes and of clones, and allocation to sexual and vegetative reproduction in the clonal herb Ranunculus reptans . We grew plants from an artificial population of R. reptans in 32 trays at two densities. After four months, differences in density were still apparent, although clones in the low-density treatment had on average 155% more rosettes and 227% more rooted rosettes than clones in the high-density treatment. The coefficient of variation of these measures of clone size was 15% and 83% higher, respectively, in the low-density treatment. This indicates that intraspecific competition among clones of R. reptans is symmetric and increases the effective population size. Rooted rosettes were larger and varied more in size in the low-density treatment. The relative allocation of the populations to sexual and to vegetative reproduction was 19% and 13% higher, respectively, in the high-density treatment. Moreover, seeds produced in the high-density treatment had a 24% higher mass and a 7% higher germination percentage. This suggests that with increasing density, allocation to sexual reproduction increases more than allocation to vegetative reproduction in R. reptans , which corresponds to the response of some other species with a spreading growth form but not of species with a compact growth form. We conclude that intraspecific competition is an important factor in the life-history evolution of R. reptans because intraspecific competition affects its clonal life-history traits and may affect evolutionary processes such as genetic drift and selection through its effect on the effective population size.     

Temporal but not spatial environmental variation drives adaptive offspring sex allocation in a plural cooperative breeder

Cooperatively breeding birds have been used frequently to study sex allocation because the adaptive value of the sexes partly depends upon the costs and benefits for parents of receiving help. I examined patterns of directional sex allocation in relation to maternal condition (Trivers-Willard hypothesis), territory quality (helper competition hypothesis), and the number of available helpers (helper repayment hypothesis) in the superb starling, Lamprotornis superbus, a plural cooperative breeder with helpers of both sexes. Superb starlings biased their offspring sex ratio in relation to prebreeding rainfall, which was correlated with maternal condition. Mothers produced relatively more female offspring in wetter years, when they were in better condition, and more male offspring in drier years, when they were in poorer condition. There was no relationship between offspring sex ratio and territory quality or the number of available helpers. Although helping was male biased, females had a greater variance in reproductive success than males. These results are consistent with the Trivers-Willard hypothesis and suggest that although females in most cooperatively breeding species make sex allocation decisions to increase their future direct reproductive success, female superb starlings appear to base this decision on their current body condition to increase their own inclusive fitness.     

Thermal dependence of reproductive allocation in a tropical lizard

In ectotherms, environmental temperature is the most prominent abiotic factor that modulates life-history traits. We explored the influence of environmental temperature on reproduction in the Madagascar ground gecko (Paroedura picta) by measuring reproductive traits of females at constant temperatures (24, 27, 30 °C). Females of this species lay clutches of one or two eggs within short intervals. For each female, we measured egg mass for the first five clutches. For one clutch, we also measured the energetic content of eggs via bomb calorimetry. Temperature positively influenced the rate of egg production, but females at 30 °C laid smaller eggs than did females at either 24 or 27 °C. Dry mass of eggs scaled allometrically with wet mass, but this relationship was similar among thermal treatments. Females at all temperatures produced eggs with similar energy densities. Females at 24 °C allocated less energy per time unit (≈8 mW) to reproduction than did females from higher temperatures (≈12 mW). However, females at either 24 or 27 °C allocated significantly more energy per egg than did females at 30 °C. Our results demonstrate that a complex thermal sensitivity of reproductive rate can emerge from distinct thermal sensitivities of egg size, egg composition and clutch frequency.     

Between-population variation in size-dependent reproduction and reproductive allocation in Pinguiculavulgaris (Lentibulariaceae) and its environmental correlates

Several important fitness components in herbaceous perennial plants are commonly related to plant size: flowering probability, reproductive allocation and fecundity. However, evidence for such size-dependence of fitness components is mostly anecdotal and unconnected to other life history traits. Here we report size-dependence for flowering probability and reproductive allocation in 11 populations of Pinguicula vulgaris and relate it to environmental factors. Flowering probability was size-dependent in all populations of P. vulgaris , and indicated the existence of a threshold size for reproduction. Populations at low altitudes and in wet soils showed a significantly higher threshold size for reproduction. Reproductive mass was also size-dependent in all populations. We found considerable between-population differences in the slope and the intercept of the regression between plant size and reproductive mass. This variation was weakly related to the environmental factors measured. In general, relationships between different size-dependent fitness components were low. Instead of showing a covariation of traits, in line with interpretations in terms of life history "tactics", P. vulgaris seemed to independently vary each size-dependent fitness component in each locality. In particular, no significant relationship was found between threshold size for reproduction and the slope of size-dependent reproductive allocation, as predicted by previous authors. Neither we found a significant influence of somatic cost of reproduction on size-dependent fitness components.     

Life-history variation in a native perennial grass (Tridens flavus): reproductive allocation,biomass partitioning,and allometry

Plant Ecology - Investment of limited resources into reproduction is a common feature of plants; coadapted life-history traits function as adaptations that have evolved to maximize fitness. There...     

Genetic variation in patch time allocation in a parasitic wasp

1. The intra-patch experience acquired by foraging parasitoid females has often been considered to have a strong influence on their tendency to leave a patch, and thus on their total patch residence time. Most studies that have been performed on this subject suggest that the patch-leaving rules observed are adaptive because they enable the females to adjust their patch residence time to local environmental conditions.
2. Considering a behavioural rule as being adaptive supposes that it has been progressively settled by natural selection, and thus that there is, in the population, genetic variation on which the natural selection could act.
3. Therefore, this study aimed to discover whether there was indeed genetic variability in the patch-leaving decision rules in a population of the egg parasitoid species Telenomus busseolae , which attacks patches of its hosts, the eggs of Sesamia nonagrioides . Different wasp families were compared using the isofemale lines method, and the behavioural records were analysed by means of a modified version of the Cox's proportional hazards model proposed by Haccou et al . (1991 ) and Hemerik, Driessen & Haccou (1993 ).
4. The results obtained show that T. busseolae females increase their tendency to leave the patch after each successful oviposition. Each host rejection also led to an increase in the tendency to leave the patch, but this effect was smaller when host rejections were observed between two ovipositions occurring in rapid succession. Subsequent visits to the patch also increased the patch-leaving tendency.
5. Genetic variability was found in both the global patch-leaving tendency and in the effect that successful ovipositions and host rejections have on this tendency.
6. The adaptive and evolutionary consequences of these results are discussed.     

Production-dependent reproductive allocation of a tall tree speciesQuercus serrata

The reproductive allocation (allocation of net production to acorns) of a tall tree speciesQuercus serrata was estimated by a method combining branch diameter distribution and the sampling of acorns per branch. Acorn production per branch of 0.5-cm diameter significantly varied among individuals and years, but not significantly across tree size. Leaf production per branch of 0.5-cm diameter had little annual fluctuation, while that of acorns fluctuated about 6 times between the maximum and minimum. The reproductive allocation was regressed against vegetative allocation, following the general model of klinkhameret al. (1992); the reproduction had a beginning threshold and reproductive allocation increased drastically at relatively young stage after the tree began reproduction. With its small threshold production, coppicing traits and large maximum size,Q. serrata seemed adaptive to infrequent but large-scale disturbances like fires.     

Density-dependent variation in reproductive success in a terrestrial orchid

 Within population variation in plant density can affect reproductive success and breeding systems. We examined such effects in Listera cordata R. Br., a north temperate terrestrial orchid, in a subalpine population in Colorado, USA. Hand pollinations showed that L. cordata was self-compatible as all pollinations produced fruits. Cross-pollinations differed significantly from self-pollinations, and had a higher number of seeds per capsule and higher % of fertilized ovules. Together they could compensate for the transmission advantage of self-pollinations. Average number of flowers per inflorescence was 4.2–4.4 and average fruit set was 20.7–23.7%. By establishing 36 plots with varying plant densities (1, 4, 8 and 16) and emasculating all flowers in target plants of a set of 20 plots, we estimated density effects on fruit and seed production. Plant density had no effect on the amount of reproduction except in reduced seed production of highly dispersed plants. Our results suggest that inbreeding depression may be an important selective factor in L. cordata. Further studies are needed to define its role in the evolution of mating systems in this species. Received February 21, 2000 Accepted December 26, 2000     

Temporal metabolic rate variation in a continental Antarctic springtail

Terrestrial systems in Antarctica are characterized by substantial spatial and temporal variation. However, few studies have addressed the paucity of data on metabolic responses to the unpredictable Antarctic environment, particularly with regard to terrestrial biota. This study measured metabolic rate variation for individual springtails at a continental Antarctic site using a fiber-optic closed respirometry system incorporating a custom-made respiration chamber. Concurrent measures of (behavioural) activity were made via daily pitfall counts.Metabolic rate of Gomphiocephalus hodgsoni measured at constant temperature varied systematically with progression through the austral summer, and was greatest mid-season. This finding of clear intra-seasonal and temperature-independent variation in mass-specific metabolic rate in G. hodgsoni is one of very few such reports for a terrestrial invertebrate (and the only such study for Antarctica), and parallels physiological studies in the Antarctic marine environment linking metabolic rate elevation with biological function rather than temperature adaptation per se. However, response to temperature at relatively short time-scales is also likely to be an important part of the life history strategy of Antarctic terrestrial invertebrates such as G. hodgsoni, which appears capable of both physiologically and behaviourally ‘tuning’ in to short-term thermal variability to respond appropriately to the local unpredictable Antarctic habitat.     

Age-related reproductive variation in a wild marine mammal population

Life history theory predicts a change in reproduction success with age as energy resources are limited and must be allocated effectively to maximize reproduction and survival. In this study, we use three reproductive performance measures, maternal expenditure, offspring weaning mass, and first-year survival, to investigate the role that maternal age plays in successful reproduction. Long-term uninterrupted life history data available for Marion Island’s southern elephant seals and mass change estimates from photogrammetry data allow for assessment of age-related reproduction performance and trade-offs. Known-aged adult females were photographed for photogrammetric mass estimation (n = 29) and their pups weighed at weaning during the 2009 breeding season. Maternal age and proportional mass loss positively influenced pup weaning mass. In turn, first-year pup return rates (as a proxy for survival) were assessed through the intensive mark–recapture program. Pup survival increased with female age and weaning mass. Pups of young females aged 3–6 years have a lower first-year survival probability compared with pups of older and larger females.     

Temporal variation in saproxylic beetle assemblages in a Mediterranean ecosystem

One of the main challenges in biological conservation has been to understand species distribution across space and time. Over the last decades, many diversity and conservation surveys have been conducted that have revealed that habitat heterogeneity acts as a major factor that determines saproxylic assemblages. However, temporal dynamics have been poorly studied, especially in Mediterranean forests. We analyzed saproxylic beetle distribution at inter and intra-annual scales in a “dehesa” ecosystem, which is a traditional Iberian agrosilvopastoral ecosystem that is characterized by the presence of old and scattered trees that dominate the landscape. Significant differences in effective numbers of families/species and species richness were found at the inter-annual scale, but this was not the case for composition. Temperature and relative humidity did not explain these changes which were mainly due to the presence of rare species. At the intra-annual scale, significant differences in the effective numbers of families/species, species richness and composition between seasons were found, and diversity partitioning revealed that season contributed significantly to gamma-diversity. Saproxylic beetle assemblages exhibited a marked seasonality in richness but not in abundance, with two peaks of activity, the highest between May and June, and the second between September and October. This pattern is mainly driven by the seasonality of the climate in the Mediterranean region, which influences ecosystem dynamics and imposes a marked seasonality on insect assemblages. An extended sampling period over different seasons allowed an overview of saproxylic dynamics, and revealed which families/species were restricted to particular seasons. Recognizing that seasons act as a driver in modelling saproxylic beetle assemblages might be a valuable tool in monitoring and for conservation strategies in Mediterranean forests.     

Comparative statics of joint reproductive allocation

We perform a perturbation analysis (comparative statics) of how optimal reproductive effort and per offspring investment are jointly affected by different selective factors. The factors considered are: (1) mortality sources, classified according to affected stage (juvenile or adult) and to its nature (avoidable or unavoidable), and (2) resource (energy) availability for the adult individual. The joint approach reveals both direct and indirect effects of each selective pressure. These interactive effects spring from the nonlinearity of reproductive expenditure, separated into a part devoted to endowing offspring (provisioning cost) and another part invested to make reproduction possible (requisite cost). The latter is envisioned as a reverse sigmoid function of fecundity (most models, so far, have considered only the first kind of cost). The indirect effects have the consequence of enlarging the class of selective pressures that can induce changes of offspring size and clutch size, as compared with current explanations. So, they illuminate new causes for some effects, and show new effects for some well-known selective causes. Several joint patterns in the two variables, shown by animals and plants in the field, can thus be given more appropriate interpretations than traditional, piecewise, ones.     

Temporal variation in floral display size and individual floral sex allocation in racemes of Narthecium asiaticum (Liliaceae)

We analyzed the effects of temporal variation in floral display size (number of flowers open at one time on a plant) on the rate of pollen removed and receipt of individual flowers for the sequential blooming plant Narthecium asiaticum (Liliaceae). Because of the acropetal blooming of this species, the display sizes when upper flowers opened was much greater than the display sizes when lower flowers opened. Our experiments revealed that large displays lead to a high rate of pollen removal from individual flowers, though they do not lead to a high rate of ovule fertilization. Consequently, the rate of pollen grains removed per flower by pollinators was greater in upper flowers than in lower flowers. The pattern of sex allocation in individual flowers within a raceme was consistent with such variation. Namely, both maleness [stamen mass/(stamen mass + pistil mass)] and pollen?:?ovule ratio were larger in upper flowers. We suggest that the temporal variation in display size, in addition to such factors as dichogamy and pollinator directionality, also produces variation in the probability of successful pollen transfer from individual flowers that may cause the variation in the sex allocation of individual flowers.     

Temporal variation in prehistoric Nubian crania

Much of the earlier work on the prehistory of Sudanese Nubia has emphasized discontinuity between early Nubian populations. However, recent investigations suggest the converse - that a remarkable degree of cultural and biological continuity exists among indigenous Nubian groups, perhaps as far back as the Paleolithic. Thus, cultural and biological differences between Nubian populations can be most effectively perceived as the result of in situ evolutionary development. The present analysis has two major purposes: (1) to describe the morphological differences in the craniofacial complex between indigenous Nubian populations extending from the A-Group (c. 3,400 B.C.) through the Christian (c. 1,500 A.D.) horizons; and (2) to account for these differences within an evolutionary framework. The multiple discriminant analysis of radiographically derived variables revealed a trend from a substantially lower and more elongated cranial vault to a shorter and taller vault throughout the almost 5,000 year time span. Associated with this pattern was a tendency for the face to become more inferiorly-posteriorly located with respect to the vault in the latter groups. Finally, the masseter and temporalis muscles underwent a reduction and slight relocation through time. We speculate that this trend may be associated with behavioral changes associated with transition from a hunting and gathering to a totally agricultural subsistence pattern.     

Temporal and numerical patterns of reproductive behavior in the southern green stink bug,Nezara viridula (Hemiptera: Pentatomidae)

Through hourly observations of 370 individuals in two 11-day test periods, the temporal and numerical patterns of mating and oviposition behavior inNezara viridula (L.) were investigated in the laboratory. There was large variation in copulatory durations (1–165 hr), number of copulations per individual (1–9), and timein copulo prior to oviposition (1–176 hr). Number of copulations and mean copulatory duration were negatively correlated for both sexes. Number of copulations was positively correlated with percent of total test time spent mating. Neither males nor females exhibited definitive refractory periods. Oviposition followed a marked diel periodicity.

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Zusammenfassung Das Paarungs- und Eiablageverhalten vonNezara viridula (Hemiptera: Pentatomidae) wurde im Labor beobachtet. Es wurden 370 markierte. Wanzen während zwei 11-tägigen Versuchen berücksichtigt. Die in kleinen Käfigen eingeschlossenen Insekten wurden einmal pro Stunde kontrolliert. Die jeweilige Kopulationsdauer für alle Paare wurde registriert, wie auch die Trennungszeiten der Individuen. Die Dauer der Kopulation schwankte von 1 bis 165 Stunden; die Individuen paarten sich 1 bis 9 mal; bei den Weibchen betrug die Gesamtpaarungszeit vor der Eiablage 1 bis 176 Stunden. Für die beiden Geschlechter verringerte sich jede einzelne Kopulationsdauer, sobald die Paarungshäufigkeit zunahm. Je niedriger die Kopulationsrate war, desto geringer war auch die gesamte Kopulationszeit (Fig. 2). Es wurden weder für die Männchen noch für die Weibchen bestimmte Inaktivitätszeiten registriert; manche blieben für längere Zeit ohne weitere Paarungen, während andere sich sofort wieder paarten. Die Eiablage fand hauptsächlich von 18.00–21.00 Uhr statt (Fig. 3).

     

Temporal variation in morphine-mast cell interaction

The possible rhythmic interaction between morphine and mast cell was investigated in mice. It has been found that both at normal and drug-induced state, mast cells varied as a function of time and the number of mast cells was significantly affected at the time in which the number of mast cells was highest over a 24-h period. The exact underlying mechanism of the phenomenon still remains to be investigated.     

Egg size and reproductive allocation in eusocial thrips

Reproductive allocation, in terms of fecundity and egg size,has been given little consideration in eusocial societies. Tobegin to address this, absolute and body size–adjustedegg volumes were compared, along with fecundity, between thefoundress and her subfertile soldier offspring in the eusocial,gall-inducing thrips, Kladothrips hamiltoni, Kladothrips waterhousei,and Kladothrips habrus, and a congeneric, Kladothrips morrisi,with fully fecund soldiers. Soldiers produced significantlylarger eggs than the foundress in all species except K. morrisi,where egg volumes did not differ. After accounting for bodysize, soldiers produced significantly smaller eggs than thefoundress in K. morrisi and marginally so in K. waterhousei,but egg sizes did not differ in K. hamiltoni and K. habrus.When egg size and fecundity data are combined, K. morrisi soldiersinvest less in reproduction than the foundress, and in conjunctionwith other life-history features the species can be consideredeusocial. Maximum likelihood analyses reveal relatively lowreproductive allocation skew in the ancestral lineages and highskew in the derived lineages, but the trend is not significantwhen fecundity and egg size are considered separately. Gallsize covaried negatively with soldier-to-foundress relativebody size–adjusted egg size and reproductive allocationand marginally so with fecundity, suggesting that gall sizeis a determinant of egg size and fecundity trade-offs in eusocialthrips and providing the strongest support to date that gallsize has featured in the social evolution of this clade. Thisstudy highlights that data on fecundity alone may be insufficientfor assessing reproductive division of labor.