Resource allocation in offspring provisioning: an evaluation of the conditions favoring the evolution of matrotrophy

We used analytic and simulation models to determine the ecological conditions favoring evolution of a matrotrophic fish from a lecithotrophic ancestor given a complex set of trade-offs. Matrotrophy is the nourishment of viviparous embryos by resources provided between fertilization and parturition, while lecithotrophy describes embryo nourishment provided before fertilization. In fishes and reptiles, embryo nourishment encompasses a continuum from solely lecithotrophic to primarily matrotrophic. Matrotrophy has evolved independently from lecithotrophic ancestors many times in many groups. We assumed matrotrophy increased the number of offspring a viviparous female could gestate and evaluated conditions of food availability favoring lecithotrophy or matrotrophy. The matrotrophic strategy was superior when food resources exceeded demand during gestation but at a risk of overproduction and reproductive failure if food intake was limited. Matrotrophic females were leaner during gestation than lecithotrophic females, yielding shorter life spans. Our models suggest that matrotrophic embryo nourishment evolved in environments with high food availability, consistently exceeding energy requirements for maintaining relatively large broods. Embryo abortion with some resorption of invested energy is a necessary preadaptation to the evolution of matrotrophy. Future work should explore trade-offs of age-specific mortality and reproductive output for females maintaining different levels of fat storage during gestation.     

Costs of anorexia during pregnancy in a viviparous snake (Vipera aspis)

Spontaneous anorexia has been documented in various animal species and is usually associated with activities competing with food intake. In natural conditions, most female aspic vipers (Vipera aspis) stop feeding during the two months of pregnancy. We carried out a simple experiment on 40 pregnant females to determine whether anorexia was obligatory or facultative, and to investigate the energetic consequence of fasting on post-partum body condition and litter traits. Three diet treatments were applied during gestation: no food, one feeding occasion, and two feeding occasions. Twelve nonpregnant, unfed females were used as a control group. Most gravid females accepted captive mice during gestation, suggesting that anorexia reported in the field was a side effect of the tremendous changes in activity pattern associated with pregnancy. Mass loss was high for unfed reproductive females, indicating high energy expenditure associated with embryo maintenance. Prey consumption allowed compensation for metabolic expenditure and enhanced post-partum female body condition, but had no effects on litter characteristics. The magnitude of the metabolic expenditure during gestation appeared to be independent of fecundity.     

Evaluation of heart malformations in B6C3F1 mouse fetuses induced by in utero exposure to methyl chloride

C57BL/6 female mice impregnated by C3H males mice to produce B6C3F1 fetuses were exposed daily for six hr to atmospheres containing 0, 250, 500, or 750 ppm methyl chloride, from gestation day 6 to gestation day 18. There were 74 to 77 females with copulation plugs per exposure concentration. Females exposed to 750 ppm ethyl chloride exhibited ataxia commencing on the seventh day of exposure (gestation day 12). They also showed hypersensitivity to touch or sound, tremors and convulsions. Six females in the 750 ppm group died and one was euthanized in extremis prior to scheduled sacrifice. On gestation day 18, all other females were euthanized for evaluation. Only dams exposed to 750 ppm exhibited significant decrease in body weight by gestation day 18, weight gain during the gestation period, and absolute weight gain (weight gain minus gravid uterine weight) versus controls. There were no treatment related-effects on these parameters in the other exposure groups. None of the groups exhibited exposure-related differences in pregnancy rate, gravid uterine weight, or maternal liver weight. There were no differences in the numbers of implantations, resorption, dead fetuses, nonlive (dead plus resorbed) fetuses, live fetuses, sex-ratio, or mean fetal body weight per litter. There was a significant exposure-related increase in the number and percentage of affected (nonlive plus malformed) fetuses per litter with the incidence of affected fetuses in the 750 ppm group significantly higher than controls. There was a statistically significant increase in the incidence of heart defects in the 500 and 750 ppm group relative to controls. Of the 37 fetuses in the study with heart defects, 23 were females, 14 were males. The heart defects observed included: absent or abnormal tricuspid valve, reduced number of papillary muscles and/or chordae tendineae on the right side, small right ventricle, globular heart, and white spots in the left ventricular wall. Multiple malformations were observed in one fetus from the 500 ppm group and in three fetuses in the 750 ppm group. It is concluded that methyl chloride inhalation exposure to pregnant C57BL/6 mice from gestation day 6 through gestation day 17 resulted in maternal toxicity only at the 750 ppm exposure concentration and was teratogenic to B6C3F1 conceptuses at exposure concentrations of 750 and 500 ppm, leading to fetal heart malformations. No evidence of embryo or fetotoxicity other than teratogenicity was seen at any of the exposure concentrations employed. No maternal, embryo or fetotoxicity or teratogenicity was associated with exposure of mice, during critical periods of embryo and fetal development, to 250 ppm of methyl chloride.     

Status of oocytes and embryos of X-autosome translocation carrier sows

The impact of an X-autosome translocation t(Xp+; 14q-), on ovulation, fertilization and embryo survival in carrier sows, was examined and compared with these parameters of normal sows. Corpora lutea counts during week-2 and week-4 of gestation were similar in normal and carrier sows (14.4 +/- 1.36 and 15.5 +/- 2.18) although embryo recovery (11.0 +/- 1.87 and 6.0 +/- 1.47) was lower than that from normal sows (12.8 +/- 1.46 and 11.5 +/- 0.87), at these stages. Among the embryos karyotyped from the week-2 embryos of carrier sows, 42% were normal, 26.4% were carriers and 31.6% were of unbalanced chromosome make-up, and of the week-4 embryos of carriers, 33.3% were normal, 57.1% were carriers and 9.1% were chromosomally unbalanced females. The preponderance of females among the unbalanced embryos recovered at week-2 of gestation (11_ and 1_) and the total absence of males among those recovered at week-4, suggest that oocytes with unbalanced chromosome constitution are eliminated before week-2 of gestation if they are fertilized by Y bearing sperm, and that the unbalanced oocytes fertilized by X bearing sperm survive up to the peri-attachment stage even though all chromosomally unbalanced embryos are eliminated before term regardless of their sex.     

Comparison of noninvasive methods for the evaluation of female reproductive condition in a large viviparous lizard,Tiliqua nigrolutea

We compared the diagnostic value of three noninvasive methods (radiography, ultrasound, and palpation) of evaluating reproductive status in females of a large viviparous skink, the blotched blue‐tongued lizard (Tiliqua nigrolutea). Radiography could be used to identify postovulatory females during the periovulatory period. However, in early to mid‐gestation, radiography did not allow differentiation of the relatively homogenous structures within the abdomen. In late gestation, once calcification of the embryonic skeleton had occurred, gestation could be diagnosed and embryos counted. Ultrasound allowed differentiation between preovulatory, postovulatory, and nonreproductive females during the periovulatory period. Ultrasound also allowed visualisation of follicles during the early and middle stages of gestation. However, the level of operator experience, and the misdiagnosis of artefacts limited the accuracy of diagnosis. In the later stages of gestation, ultrasound did allow the detection of identifiable features of the developing foetal unit (fluid‐filled foetal membranes, independent movement of the embryo, and visualisation of the heartbeat). Colour Doppler imaging could be used to visualise embryonic blood flow. Ultrasonography was not useful in detecting the number of embryos present. Palpation during the periovulatory period could be used to detect follicles and determine whether ovulation had occurred. However, during the remainder of the gestation period, palpation was unable to differentiate reproductive condition. This study provides a basis for the diagnosis of reproductive condition and problems in viviparous reptiles. Each of the diagnostic techniques is useful at different stages of gestation, and the use of a combined approach will give the most information throughout the reproductive cycle. Zoo Biol 21:253–268, 2002. © 2002 Wiley‐Liss, Inc.     

The tight junctional protein occludin is found in the uterine epithelium of squamate reptiles

Occludin, an integral protein associated with the mammalian tight junction, has for the first time been identified in the uterus of squamate reptiles. The tight junction is made up of anastamosing strands and forms a selective barrier that regulates paracellular diffusion of solutes across uterine epithelium. Occludin exclusively labels tight junctional strands and is an excellent marker for tight junction permeability. Using western blotting and immunohistochemistry, occludin expression was examined in the uterine epithelium of five species of Australian skinks at different stages of gestation. More occludin was detected during late stage pregnancy/gravidity compared to the lower levels of occludin detected in vitellogenic and post-parturient females in three of the five species. We conclude that the paracellular permeability of the squamate uterine epithelium decreases as gestation progresses. As placental transport of ions and solutes to the embryo is highest during the last third of pregnancy in viviparous squamates, it is likely that a decrease in paracellular permeability is compensated by an upregulation of other transporting mechanisms such as histotrophy.     

Reproductive biology of the smooth-hound shark Mustelus mustelus (L.) in the Gulf of Gabès (south-central Mediterranean Sea)

The reproductive biology of the smooth-hound shark Mustelus mustelus was studied in the Gulf of Gabès (southern Tunisia). Females were found to mature between 1075 and 1230 mm total length ( L _T) whereas males matured between 880 and 1120 mm L _T. The L _T at which 50% of the population reached maturity was 971 and 1172 mm for males and females, respectively. Male gonads were symmetrical in terms of mass and both functional, whereas in females only the right ovary was functional. The seasonal changes in the oocytes and testes development, embryo length and the occurrence of near-term and post-partum females showed that this species displayed a clearly defined annual reproductive cycle with parturition occurring during late April and early May, after a gestation period of 10–11 months. Mating took place during May and early June and fertilization occurred from early June to early July. The embryo sex ratio was not significantly different from unity. Litter size varied from four to 18 embryos and was positively correlated with maternal L _T. The young were born with a L _T of 340–420 mm.     

Developmental stages and chemical composition in embryos of the cockroach, Diploptera punctata, with observations on the effect of diet

A developmental time-table has been established for the embryos of viviparous Diploptera punctata. The percentage of gestation time occupied by pre-dorsal closure stages is only 19 per cent compared to 40 or 50 per cent in non-viviparous species. The increase in wet weight of the embryos begins several days before dorsal closure and continues throughout gestation. The increase in dry weight, protein, carbohydrate, and uric acid does not begin until shortly after dorsal closure but thereafter parallels the increase in wet weight.The increase in oöcyte protein during vitellogenesis is tenfold, less than in oviparous or ovoviviparous species. But the increase in embryo protein during gestation is sixtyfold; this characterizes viviparity in D. punctata.Although total lipid increases during gestation, lipid as a percentage of wet weight decreases most rapidly before dorsal closure and less rapidly there-after. It is suggested that before dorsal closure lipid is the major energy source for development. After dorsal closure the embryos are able to drink through their mouths the fluid nutrient provided by the mother.The ultimate source of nutrients required by developing embryos is the maternal diet during gestation. Females starved from ecdysis do not produce young; females fed only sugar from ecdysis produce viable larvae but suffer loss in body weight. Embryos from such females, although normal in length, are deficient in protein.     

Costs and benefits of polyandry in a placental poeciliid fish Heterandria formosa are in accordance with the parent-offspring conflict theory of placentation

In viviparous species, a conflict over maternal resource allocation may arise between mothers and embryos, between siblings, and between maternal and paternal genes within an embryo due to relatedness asymmetries. We performed two experiments to study the effects of polyandry and brood relatedness on offspring growth in a placental fish (Heterandria formosa). Polyandry was beneficial as it increased the probability of pregnancy, possibly to avoid genetic incompatibility. However, females mated to four males produced offspring that had a longer maturation time than those of monandrous females. When within-brood relatedness was manipulated, the size of the newborn offspring decreased with time in low-relatedness treatment, whereas in highly related broods, offspring size was constant. Low within-brood relatedness may lead to less cooperative offspring in terms of resource extraction from the mother, which may lead to impaired development during gestation. Offspring conflict may thus reduce the benefits of polyandry in viviparous species.     

Reproductive biology of the smooth butterfly ray Gymnura micrura

This study provides the first detailed information on the reproductive biology of the smooth butterfly ray Gymnura micrura. A total of 905 individuals were sampled, 377 of which were used for the reproductive study. Juveniles accounted for 75% of the sample, but all life cycle stages were present in the study area. The disc width at which 50% were mature (W(D50) )was estimated at 269 and 405 mm for males and females, respectively. The W(D50V) (based on the onset of vitellogenesis) was estimated at 359 mm. Uterine fecundity (mean ±s.d. = 3·8 ± 1·3; range: 1-6) was positively correlated with female size. A 3564% gain in mean wet mass was observed from egg to full-term embryo in utero. Size at birth ranged from 135 to 175 mm W(D) (19·5 to 55·0 g), with a mean of 165·1 mm W(D) (43·3 g). The embryo sex ratio was not significantly different from 1:1. The ovaries of pregnant females were undergoing vitellogenesis during gestation, with females ready to ovulate soon after parturition. Gymnura micrura may have an asynchronous reproductive cycle, with females reproducing continuously throughout the year.     

Gestation, thermoregulation, and metabolism in a viviparous snake, Vipera aspis: evidence for fecundity-independent costs

Oxygen consumption of gestating Aspic vipers, Vipera aspis (L.), was strongly dependent on body temperature and mass. Temperature-controlled, mass-independent oxygen consumption did not differ between pregnant and nonpregnant females. Maternal metabolism was not influenced during early gestation by the number of embryos carried but was weakly influenced during late gestation. These results differ from previous investigations that show an increase in mass-independent oxygen consumption in reproductive females relative to nonreproductive females and a positive relationship between metabolism and litter size. These data also conflict with published field data on V. aspis that show a strong metabolic cost associated with reproduction. We propose that, under controlled conditions (i.e., females exposed to precise ambient temperatures), following the mobilisation of resources to create follicles (i.e., vitellogenesis), early gestation per se may not be an energetically expensive period in reproduction. However, under natural conditions, the metabolic rate of reproductive females is strongly increased by a shift in thermal ecology (higher body temperature and longer basking periods), enabling pregnant females to accelerate the process of gestation. Combining both laboratory and field investigation in a viviparous snake, we suggest that reproduction entails discrete changes in the thermal ecology of females to provide optimal temperatures to the embryos, whatever their number. This results in the counterintuitive notion that metabolism may well be largely independent of fecundity during gestation, at least in an ectothermic reptile.     

小熊猫繁殖周期血清雌二醇和孕酮含量变化

为研究小熊猫繁殖周期血清雌二醇、孕酮含量变化规律,采用化学发光免疫分析法连续16 次测定了2只成体雌性小熊猫血清雌二醇和孕酮含量变化,历经发情间期、发情期和两次妊娠期;连续9次测定了7只小熊猫妊娠期的孕酮含量变化。结果:(1)发情间期,小熊猫血清雌二醇的水平一直维持在低水平(基础水平),进入发情前期,血清雌二醇水平明显升高,在发情期一直维持高水平,配种后迅速降至基础水平; (2)小熊猫血清孕酮含量在发情间期和发情期均维持在较低水平,直至发情期过后才出现升高,在妊娠期一直维持高水平,峰值出现在5 月;(3)发情的小熊猫不论妊娠与否,在妊娠期内血清孕酮含量均维持在高水平。研究表明:小熊猫血清雌二醇、孕酮含量变化能直接反映其繁殖规律,雌二醇对启动雌性小熊猫季节性繁殖起重要作用;在妊娠期内小熊猫血清孕酮含量升高不能作为判断小熊猫妊娠的标准;雌性小熊猫在妊娠期有假孕现象。     

Prenatal bias in sex ratios in a marsupial,Antechinus agilis.

Biased sex ratios of young of birds and mammals clearly occur and may have an adaptive significance, but we rarely know the stage at which a bias is generated, or the mechanism. If a bias is generated prior to birth, studies of marsupials may be insightful because gestation is short and neonates are relatively undifferentiated. This study investigated whether biased sex ratios in Antechinus agilis are generated in the brief period between birth and the attachment of young to the mother''s teats. When all young born, or just pouch young, or supernumerary young were considered, litters were strongly biased towards females (0.32 males), and there was no significant difference across the groups, so a bias is generated before birth in this species. Evidence from counts of corpora lutea suggests that embryo loss during gestation cannot account fully for the level of bias observed. Therefore, prefertilization mechanisms must contribute to the generation of sex-biased litters in this marsupial.     

Presence and distribution of E-cadherin in the 4-cell golden hamster embryo. Effect of maternal age and parity

Maternal age dependency of gestation time in hamster and in other mammals is a well demonstrated fact. We have recently shown that adult nulliparous and multiparous hamster females show significant asynchrony and retard on early embryo development (from two blastomeres to morula stages) when compared with nulliparous young females. The number of cell-cell adhesions between blastomeres in early embryo development has been reported to be a good indication of the ability of embryos to cleave and develop. In this work we studied, by indirect immunofluorescence, the presence and distribution of E-cadherin in 4-cell embryos obtained from nulliparous young (NYF), nulliparous adult (NAF) and multiparous adult (MAF) hamster females. Distribution and intensity of fluorescence was observed and registered using confocal microscopy. Staining intensities for E-cadherin were quantified by computed densitometry in the free membrane regions, in the cytoplasm region and in the cell-cell adhesion zones of each embryo. E-Cadherin in all the studied zones was significantly higher (p<0.01) in NYF. Cadherin concentration in the intercellular membranes was always statistically higher (p<0.05) than in the free membrane regions. An appreciable concentration of E-cadherin was found in the cytoplasm of the 4-cell embryos obtained from the three groups of females, but was significantly higher in NYF. No statistical differences were observed in any of the parameters studied between NAF and MAF. Our results seem to indicate that changes in the reproductive behavior related to age and/or multiparity may be correlated with changes in the processes related to intercellular adhesions during early cleavage.     

Changes in temporal and spatial patterns of Gi protein expression in postimplantation mouse embryos

We previously demonstrated the presence of GTP-binding proteins, G proteins, in the preimplantation mouse embryo (Jones and Schultz, 1990. Dev. Biol. 139, 250-262). These studies have been extended to the Day 6.5, 7.5, and 8.5 gestation embryo by employing PT-catalyzed ADP-ribosylation and immunoblotting techniques. We report here that the amount of embryonic alpha i increases from Day 6.5 to Day 7.5 of gestation, and remains at about the same level at Day 8.5. In contrast, the extent of PT-catalyzed ADP-ribosylation of Gi alpha protein(s) decreases between Days 6.5 and 7.5--this decrease is global and not restricted to a particular germ layer of the Day 7.5 embryo--and then dramatically increases by Day 8.5 of gestation. In the Day 8.5 gestation embryo, the extent of PT-catalyzed ADP-ribosylation of Gi alpha proteins increases along the anterior-posterior axis, whereas the amount of immunoreactive alpha i subunit decreases along this axis. By using a combination of PT-catalyzed ADP-ribosylation and immunoprecipitation with antisera specific for alpha i1, alpha i2, or alpha i3, we report that all three alpha i subtypes are present in the Day 8.5 gestation mouse embryo. Results of these experiments suggest that an activation of Gi proteins occurs between Days 6.5 and 7.5 of gestation in the postimplantation embryo, a time during which the embryo is gastrulating, and that a decreasing gradient of activation exists along the anterior to posterior axis in the Day 8.5 gestation embryo. Last, we report that oocytes, eggs, and preimplantation embryos possess all three subtypes of alpha i.     

Experimental litter size reduction reveals costs of gestation and delayed effects on offspring in a viviparous lizard

Experimental studies have often been employed to study costs of reproduction, but rarely to study costs of gestation. Disentangling the relative importance of each stage of the reproductive cycle should help to assess the costs and benefits of different reproductive strategies. To that end, we experimentally reduced litter size during gestation in a viviparous lizard. We measured physiological and behavioural parameters during gestation and shortly after parturition, as well as survival and growth of females and their offspring. This study showed four major results. First, the experimental litter size reduction did not significantly affect the cellular immune response, the metabolism and the survival of adult females. Second, females with reduced litter size decreased their basking time. Third, these females also had an increased postpartum body condition. As postpartum body condition is positively related to future reproduction, this result indicates a gestation cost. Fourth, even though offspring from experimentally reduced litters had similar weight and size at birth as other offspring, their growth rate after birth was significantly increased. This shows the existence of a maternal effect during gestation with delayed consequences. This experimental study demonstrates that there are some costs to gestation, but it also suggests that some classical trade-offs associated with reproduction may not be explained by gestation costs.     

Farrowing rates and litter size following transfer of vitrified porcine embryos into a commercial swine herd

The objective was to determine farrowing rates and litter sizes that could be achieved in a typical farm-to-farm porcine embryo transfer program using vitrified blastocysts that were zona pellucida intact when cryopreserved. The embryos were transferred surgically on-farm into recipient sows that were managed throughout gestation and farrowing under the same conditions as other sows in the herd. Twenty recipient sows (mean parity 2.1) received a total of 568 embryos; seven received 203 embryos derived from donor sows, five received 139 embryos from gilts and eight received a mixture of 161 embryos from sows and 65 from gilts. Sixteen sows (80%) were confirmed pregnant at approximately 35 days gestation, 15 farrowed at full term (farrowing rate 75%). One sow died during gestation (with a total of 18 fetuses in utero). A total of 123 piglets were born (mean, 8.2), of which 115 were born alive (mean, 7.7). Of the 568 embryos transferred to all 20 sows, 21.6% resulted in piglets born and 29.0% survived to produce piglets in sows that farrowed. There were no significant differences in embryo survival among sow, gilt or mixed sow and gilt embryos. The ratio of males to females was 71/52 and the mean birth weight was 1.6 kg (range 0.6-2.6 kg). In conclusion, vitrified zona pellucida intact embryos can be used to transfer genetic material from farm-to-farm with acceptable reproductive performance.     

Fetometry and fetal heart rates between Day 35 and 108 in bovine pregnancies resulting from transfer of either MOET, IVP-co-culture or IVP-SOF embryos

The Large Offspring Syndrome has frequently been reported for in vitro produced calves. The objective of this study was to determine whether any differences in body dimensions (biparietal diameter of the cranium (BPD), cross-section of the abdomen at the insertion of the umbilical cord (CAU)) and heart rate (FHR) can be detected during the first 108 days of gestation between bovine foetuses derived from different methods of embryo production. Three groups of pregnancies with calvings at term resulted from non-surgical transfers of three types of embryos: recipients carrying an embryo obtained by standard MOET procedures (n = 25); recipients carrying an embryo produced in vitro from OPU-derived oocytes, using co-culture-medium (n = 14) or SOF-medium (n = 22). Transrectal ultrasonographic examinations were performed weekly. Ultrasound images were recorded and during off-line analysis FHR, BPD and CAU were determined. For each foetus a curve was fitted and the estimates on fixed time intervals were used as dependent variables in an analysis of variance to detect differences between the three pregnancy groups. Neither gestation length nor birth weight differed significantly between the three pregnancy groups, nor could any differences with respect to BPD, CAU or FHR be detected between Days 35 and 108 of gestation. It is concluded that no differences exist between the early development of bovine foetuses, derived from MOET, IVP-co-culture or IVP-SOF embryos, and resulting in calves with normal birth weights.     

Transplacental nutrient transfer during gestation in the Andean lizard <Emphasis Type="Italic">Mabuya</Emphasis> sp. (Squamata,Scincidae)

Mabuya skinks have the most specialized allantoplacenta and the greatest degree of placentotrophy known among the Reptilia. Their recently ovulated eggs are microlecithal (1–2 mm) and lack fatty yolk platelets; thus, virtually all of the nutrients for embryonic development must pass across the placenta. We quantified the net uptake of nutrients during gestation in an Andean population of Mabuya and compared these results with other matrotrophic skinks and eutherian mammals. Total dry and wet masses, ash and organic content, ions (calcium, potassium, sodium, magnesium, iron), lipids (cholesterol, vitamin E and fatty acids in the major lipid classes—triacylglycerol, phospholipids, cholesteryl ester, free fatty acids), nitrogen (an index of protein) were measured during the different developmental stages throughout gestation, and in neonates. A significant net uptake of inorganic and organic matter was found. This uptake begins slowly during early gestation but accelerates during the last third of gestation when the growth of the embryo is maximal and the allantoplacenta has developed its greatest complexity. The drastic reduction of egg size in this clade is related to the great reduction in the contribution of lecithotrophic nutrients to the embryo, an obligatory placentotrophy from early developmental stages, and the highest placental complexity known in the Reptilia. All of these features converge with features found in eutherian mammals.