Lipids and proteins in the Rathke's gland secretions of the North American mud turtle (Kinosternon subrubrum)

Lipids and proteins in the Rathke's gland secretions of the North American mud turtle (Kinosternon subrubrum, Kinosternidae) were analyzed by gas chromatography-mass spectrometry (GC-MS) and SDS-polyacrylamide gel electrophoresis (SDS-PAGE), respectively. Analysis by GC-MS indicates 2,3-dihydroxypropanal and C₃–C₂₄ free or esterified fatty acids. Analysis by SDS-PAGE indicates a major protein component with an approximate molecular mass of 60 kDa and minor components ranging from ca. 23 to 34 kDa. The major component of K. subrubrum glandular secretions exhibits a mobility that matches that of the Kemp's ridley sea turtle (Lepidochelys kempi, Cheloniidae), suggesting that these proteins are evolutionarily conserved.     

Physiological and behavioral variation in estivation among mud turtles (Kinosternon spp.)

Kinosternid mud turtles, a primarily aquatic group, exhibit variable degrees of terrestrial activity in the Sonoran and Chihuahuan Deserts. We compared behavioral and physiological responses to dry conditions in four populations representing three species, Kinosternon sonoriense, Kinosternon flavescens, and Kinosternon hirtipes. All four groups were subjected to simulated dry season conditions in the laboratory, during which activity was monitored and physiological responses (blood chemistry and rates of resting metabolism and evaporative water loss) were measured. Kinosternon flavescens and K. hirtipes represented extremes in apparent ability to estivate, based on activity and rate of increase of plasma osmolality. Two populations of K. sonoriense exhibited intraspecific differences in behavioral and physiological measures that were related to extant environmental conditions. Large numbers of K. sonoriense from Arizona and K. hirtipes, the poorest estivators, had to be rehydrated after only 30 d out of water. Kinosteron flavescens had the lowest metabolic rates, but no evidence of metabolic depression during dehydration was found for any of the four populations. We conclude that the differences in capacity for estivation among populations are primarily linked to variable behavioral responses to dry conditions, though high rates of evaporative water loss in K. hirtipes represent a probable physiological constraint.     

Terrestrial dormancy in the turtle Kinosternon flavescens: Respiratory metabolism and dehydration

Experimentally induced terrestrial dormancy resulted in reduced rates of oxygen consumption and carbon dioxide release by the turtle, Kinosternon flavescens.

• 1.2. An unusually low respiratory quotient for dormant turtles indicates retention of carbon dioxide.
• 2.3. Sharply elevated levels of oxygen consumption upon emergence from dormancy suggest payment of an oxygen debt and support previous suspicion of increased anaerobic metabolism.
• 3.4. Most of the weight lost by dormant turtles is attributed to dehydration rather than metabolism.
• 4.5. Suppressed gas exchange apparently reduces water loss from the respiratory tract, an adjustment which may be essential in avoiding severe dehydration.

     

The influence of a positive correlation between clutch size and offspring fitness on the optimal offspring size

Summary The effect is modeled of a positive relationship between clutch size and offspring fitness on the optimal investment in offspring. In species which meet the assumptions of the model, the model predicts a positive correlation between maternal resource level and offspring size. If larger mothers are able to allocate more resources to offspring, then the model would also predict a positive correlation between maternal size and offspring size when the assumptions of the model are met. Thus, this model may help explain both among and within individual variation in offspring size. When offspring are produced in groups and the number of offspring killed per clutch is limited by predator satiation, offspring in larger clutches may experience a higher probability of survival. Such a life style may be found in animals such as sea turtles. Offspring size is positively correlated with maternal size in some members of this group.     

Maternal body size as a morphological constraint on egg size and fecundity in butterflies

It is a widespread notion that in arthropods female reproductive output is strongly affected by female size. In butterflies egg size scales positively with female size across species, suggesting a constraint imposed by maternal size. However, in intraspecific comparisons body size often explains only a minor part of the variation in progeny size. We here include representatives of various butterfly families to test the generality of this phenomenon across butterflies. Phenotypic correlations between egg and maternal body size were inconsistent across species: correlations were non-significant for Pararge aegeria and Lycaena tityrus, significantly positive for Papilio machaon, significantly negative for Araschnia levana, and contradictory for Pieris napi. Thus, there was no general pattern linking egg size to maternal size, e.g., caused by an allometric relationship. Consequently, there was at best limited evidence for maternal size acting as a morphological constraint on egg size within butterfly species. Realized fecundity depended on maternal size in P. napi and A. levana, but not in P. aegeria, suggesting that maternal size may affect egg number more strongly than egg size. Yet, variation in fecundity was primarily explained by variation in longevity as is expected for income breeders. Heritability estimates across species were rather similar for pupal mass (ranging between 0.14 and 0.19), but more variable for egg size (0.17–0.31).     

Size-number trade-off and optimal offspring size for offspring produced sequentially using a fixed amount of reserves

We analysed the nature of size-number trade-off of offspring when multiple cohorts of such offspring are produced sequentially using a fixed amount of reserves. In the model, we incorporated sink-limitation in the resource absorption rate of offspring from the mother tissue and the loss of resources by maintenance respiration. We found that the later the initiation of a cohort, the greater the cost of producing a cohort with the same size and number of offspring. This is due to the loss of resources by maintenance respiration during the period from the beginning of reproduction to the initiation of the cohort. Also, the extra cost increases with an increase in the specific maintenance respiration rate. Thus, resources lost to respiration over time reduces the fitness value of producing late cohorts. Hence, it is advantageous to produce all offspring simultaneously unless there are fitness advantages of producing offspring sequential which overcome this cost or constraints preventing simultaneous production. Sequentially offspring production evolves if there is a constraint on the number of offspring of each cohort. With this constraint, the optimal offspring size decreases with the production sequence of cohorts.     

Multiple resources and the optimal balance between size and number of offspring

Summary We extend the classical Smith-Fretwell model for the optimal size of an offspring to the case of allocation of two or more fitness enhancing resources. Unlike the results of the single-resource model, the new model predicts that the optimal allocations will depend on the resource pool sizes. We apply this new model to the problem of carbon and nitrogen allocation to seeds and conclude (1) that the optimal seed size (carbon allocation) should be positively correlated with the ratio of the size of the carbon and nitrogen pools available for investment to offspring (C/N ratio) and (2) that there should be a negative correlation between seed size and absolute seed nitrogen content. These results may account for some of the within- and between-plant variation in resource allocation to seeds.     

A model for optimal offspring size in fish, including live-bearing and parental effects

Since Smith and Fretwell's seminal article in 1974 on the optimal offspring size, most theory has assumed a trade-off between offspring number and offspring fitness, where larger offspring have better survival or fitness, but with diminishing returns. In this article, we use two ubiquitous biological mechanisms to derive the shape of this trade-off: the offspring's growth rate combined with its size-dependent mortality (predation). For a large parameter region, we obtain the same sigmoid relationship between offspring size and offspring survival as Smith and Fretwell, but we also identify parameter regions where the optimal offspring size is as small or as large as possible. With increasing growth rate, the optimal offspring size is smaller. We then integrate our model with strategies of parental care. Egg guarding that reduces egg mortality favors smaller or larger offspring, depending on how mortality scales with size. For live-bearers, the survival of offspring to birth is a function of maternal survival; if the mother's survival increases with her size, then the model predicts that larger mothers should produce larger offspring. When using parameters for Trinidadian guppies Poecilia reticulata, differences in both growth and size-dependent predation are required to predict observed differences in offspring size between wild populations from high- and low-predation environments.     

Conflict between optimal clutch size for mothers and offspring in the leaf miner, Leucoptera sinuella

Abstract. 1. Clutch size in a leaf‐mining moth, Leucoptera sinuella (Reutti), was examined to determine whether the clutch size in natural populations meets the prediction of an optimal strategy, through comparisons between the optimal clutch sizes for offspring and for a mother. 2. A field experiment revealed that premature leaf abscission, egg dropping, and larval competition were important selective forces in determining the clutch size of this leaf miner on its host plant, Salix miyabeana. Then, optimal clutch size was predicted using the theoretical model of Weis et al. (1983 ), from the data obtained in the field experiment. 3. The model predicts that the clutch size that maximises offspring fitness is two, and that the clutch size that maximises reproductive success of the female varies from two to four, depending on the female's survival rate between oviposition events. The predicted clutch size (two) was identical to the clutch size observed most frequently in the field, assuming > 95% survival rate of females. Suitability of the model of Weis et al. (1983 ) was discussed based on these results.     

State-dependent life-history theory and its implications for optimal clutch size

Summary Life-history theory is usually based on an animal's age or size. McNamara describes a general technique for finding the optimal life-history when an organism's strategy is allowed to depend on other aspects of its state. In this paper we describe the technique in the context of previous work in life-history theory and discuss how it can be used to look at decisions on a finer time scale than the usual annual decisions. We show how it can be used to model optimal clutch size when there is a trade-off between number and quality of offspring. It is shown that the optimal clutch size is typically less than the most productive clutch size. Measuring the value of a clutch in terms of the number of offspring that survive to breed or even the number of grandchildren that survive to breed may give misleading results.     

Effect of temperature on metabolic rate of the mud turtle (Kinosternon subrubrum)

Temperature plays an important role in various aspects of the life history and physiology of ectotherms. We examined the effect of temperature on standard metabolic rate in the mud turtle, Kinosternon subrubrum. We measured O₂ consumption and CO₂ production at 20°C and 30°C using a flow through respirometery system. Standard metabolic rate was significantly higher at 30°C (9.25 ml O₂/h, 6.35 ml CO₂/h) compared to 20°C (2.10 ml O₂/h, 1.96 ml CO₂/h). The Q₁₀ value for O₂ was 5.10, and for CO₂ was 3.40. Our findings generally agree with those of other studies of metabolism in vertebrate ectotherms.     

Effect of maternal foraging habitat on offspring quality in the loggerhead sea turtle (Caretta caretta)

Exploring a trade‐off between quantity and quality of offspring allows differences in the fitness between alternative life histories to be accurately evaluated. We addressed the mechanism that maintains alternative life histories (small oceanic planktivores vs. large neritic benthivores) observed in a loggerhead sea turtle (Caretta caretta) population, which has been suggested to be environmental, based on the lack of genetic structure and a large difference in reproductive output. We examined whether maternal foraging habitat affects offspring quality, by measuring the morphology, emergence success, and righting response of hatchlings following incubation in a common open sand area over the whole nesting season at Yakushima Island, Japan, and by recording early growth and survival of offspring that were reared in a common environment at a Japanese aquarium. Furthermore, we tested whether sea turtles adjust egg size in response to temporal shifts of the incubation environment. There were no significant differences in any hatchling traits between oceanic and neritic foragers (which were classified by stable isotope ratios), except for clutches laid during the warmest period of the nesting season. There were also no significant differences in the growth and survival of offspring originating from the two foragers. The size of eggs from both foragers significantly increased as the season progressed, even though the rookery had heavy rainfall, negating the need to counteract heat‐related reduction in hatchling morphology. In comparison, the sizes of adult body and clutches from both foragers did not vary significantly. The results further support our previous suggestions that the size‐related foraging dichotomy exhibited by adult sea turtles does not have a genetic basis, but derives from phenotypic plasticity. Adjustment in reproductive investment may be associated with: (1) predation avoidance, (2) founder effect, and/or (3) annual variation in egg size.     

A general model for the scaling of offspring size and adult size

Understanding evolutionary coordination among different life-history traits is a key challenge for ecology and evolution. Here we develop a general quantitative model predicting how offspring size should scale with adult size by combining a simple model for life-history evolution with a frequency-dependent survivorship model. The key innovation is that larger offspring are afforded three different advantages during ontogeny: higher survivorship per time, a shortened juvenile phase, and advantage during size-competitive growth. In this model, it turns out that size-asymmetric advantage during competition is the factor driving evolution toward larger offspring sizes. For simplified and limiting cases, the model is shown to produce the same predictions as the previously existing theory on which it is founded. The explicit treatment of different survival advantages has biologically important new effects, mainly through an interaction between total maternal investment in reproduction and the duration of competitive growth. This goes on to explain alternative allometries between log offspring size and log adult size, as observed in mammals (slope = 0.95) and plants (slope = 0.54). Further, it suggests how these differences relate quantitatively to specific biological processes during recruitment. In these ways, the model generalizes across previous theory and provides explanations for some differences between major taxa.     

Experimental (antiestrogen-mediated) reduction in egg size negatively affects offspring growth and survival

The relationship between egg size and offspring phenotype is critical to our understanding of the selective pressures acting on the key reproductive life-history traits of egg size and number. Yet there is surprisingly little empirical evidence to support a strong, positive relationship between egg size and offspring quality (i.e., offspring growth, condition, and survival) in birds, in part because of confounding effects of parental quality and the lack of experimental techniques for directly manipulating avian egg size independently of maternal condition. Previously, we showed that treatment of laying female zebra finches (Taeniopygia guttata) with the antiestrogen tamoxifen can decrease egg size by ca. 8% but that this reduction in egg size had few effects on offspring mass and size at fledging. Here, we extend the use of this technique to induce larger decreases in egg size (up to 50% in individual females) and show that a reduction in egg size of ca. 18% is associated with decreased embryo viability, increased hatchling mortality, and lower posthatching offspring survival. Furthermore, we show that although hatchlings from eggs reduced in size by ca. 9% can survive to fledging, these chicks show slower initial growth during the linear growth phase (5-10 d of age), fledge at lower masses than chicks from control eggs, and show postfledging compensatory growth. Our results provide empirical support for significant effects of egg size on offspring quality and further suggest that among individual females there is a minimum egg size required to maintain embryo viability and offspring quality.     

Evidence for prenatal transfer of rabies virus in the Mexican free-tailed bat (Tadarida brasiliensis Mexicana)

Fetuses were collected from four Mexican free-tailed bats (Tadarida brasiliensis mexicana) and a fetal bat cell (FBC) line was established and tested for its ability to support the replication of the ERA vaccine strain of rabies virus. Cytopathic effects were detected in ERA virus-inoculated as well as uninoculated FBC's. Immunofluorescent antibody testing of uninoculated FBC's provided no evidence for the presence of rabies virus. However, mice inoculated intracranially with supernatant fluid from uninoculated FBC's died. Enzyme-linked immunosorbent assay and immunofluorescent antibody testing revealed rabies virus in the brains of these mice. Tests with a panel of monoclonal antibodies indicated that the isolate was the same as that isolated from Mexican free-tailed bats from the southwestern United States. We conclude that the fetuses from which the FBC line was derived had been infected in utero with rabies virus. We believe this may represent the first observation of prenatal transfer of rabies virus in naturally infected bats.     

Heteroblasty and preformation in mayapple, Podophyllum Peltatum (Berberidaceae): developmental flexibility and morphological constraint

Developmental preformation can constrain growth responses of shoots to current conditions, but there is potential for flexibility in development preceding formation of the preformed organs. Mayapple (Podophyllum peltatum) is strongly heteroblastic, producing rhizome scales, bud scales, and either a single vegetative foliage leaf or two foliage leaves on a sexual shoot. To understand how and when preformation constrains growth responses, we compare (1) how leaf homologs of the renewal shoot differ in development, (2) whether there are differences in shoot development that occur in advance of morphological determination of shoot type, and (3) whether there are points of developmental flexibility in renewal shoot growth prior to preformation of the foliage and floral organs. We use scanning electron microscopy and histology to show that the three vegetative leaves (both types of scale leaves and the vegetative foliage leaf) are similar in the initial establishment of an encircling and overarching leaf base. Differences among them are found in the timing of differentiation of the leaf base and in the relative timing and degree of growth of the lamina and petiole. In contrast, foliage leaves on sexual shoots show less expression of the leaf base and precocious growth of the lamina and petiole. Prior to shoot type determination, there are no morphological differences in the sequence or position of leaf homologs that predict final shoot type. In this colony, leaves at positions 12 and 13, on average, appear to be identical in development until they are between 700 and 800 μm in length, when it becomes possible to distinguish leaves that will become vegetative foliage leaves from additional bud scale leaves on vegetative or sexual shoots. We suggest that late developmental determination of leaves at positions 12 and 13 reflects ontogenetic sensitivity to a transition to flowering. Thus, in mayapple, heteroblasty appears to facilitate developmental flexibility prior to the point where shoot growth becomes constrained by preformation of determined aerial structures.     

Within-plant variation in seaweed palatability and chemical defenses: optimal defense theory versus the growth-differentiation balance hypothesis

Within-plant variation in the concentration of secondary metabolites, nutritive value, toughness, and susceptibility to herbivory was assessed for the brown alga Dictyota ciliolata. When young apices and older tissue from the same plant were offered in equal abundance to the herbivorous amphipod Ampithoe longimana and the sea urchin Arbacia punctulata, young apices were consumed about 2 times more than older tissue. Compared to young apices, the less preferred older tissue had a less palatable lipophilic extract, significantly higher concentrations of two secondary metabolites (another secondary metabolite did not differ significantly), 33% more soluble protein, and was 233% tougher. Higher levels of chemical defenses in older tissues, and not tissue toughness or nutritive value, appear to be responsible for the preference of Ampithoe longimana for young apices. The pattern of lower levels of chemical defenses in young than older tissues of D. ciliolata is the opposite of the pattern observed in coenocytic seaweeds and most vascular terrestrial and marine plants, all of which have translocation systems for moving materials among plant portions. Unlike these other plants, which preferentially allocate chemical defenses to young tissues, D. ciliolata cannot readily translocate secondary metabolites. The growth-differentiation balance hypothesis suggests that actively dividing and expanding cells are less able to produce secondary metabolites. This hypothesis may help explain why older tissues are better defended than young, rapidly growing apices.