Effects Of Maternal Size Research Articles

Effect of Maternal Size, Reproductive Season and Interannual Variability in Offspring Provisioning of Carcinus maenas in a Coastal Lagoon

Maternal effects and larval experience are considered the most important sources of variability in offspring phenotypes in marine invertebrates. Maternal provisioning during oogenesis is the first of a series of processes that will ultimately affect offspring phenotype and population dynamics. The keystone species of several European estuarine environments, Carcinus maenas, was used as a model to analyse the effect of female size and reproductive season on the fatty acid (FA) profile of newly extruded (stage 1) and ready-to-hatch (stage 3) embryos, as proxies for maternal investment and quality of newly hatched larvae, respectively. A total of 60 ovigerous females of two different sizes (carapace width [CW]: small CW <40 mm; large CW ≥40 mm) from Ria de Aveiro (Portugal) were sampled during three different reproductive periods: early reproductive season (ERS, late March/early April) 2012, ERS-2013 and late reproductive season (LRS; July) 2013. Maternal size was not a reliable indicator of maternal provision or larval quality at hatching. The interannual comparison (ERS-2012 vs. ERS-2013) revealed that the FA profile of stage 3 embryos was likely shaped by environmental conditions in the coastal lagoon during incubation. The seasonal comparison (ERS-2013 vs. LRS-2013) showed that embryos in the LRS had higher quality lipid content than embryos in the ERS, suggesting an increase of energetic reserves destined for reproduction in females in the LRS. Studies on maternal investment that overlook temporal variability should be interpreted with caution, especially in species inhabiting highly dynamic environments such as coastal lagoons and estuaries.

Fitness consequences of early life conditions and maternal size effects in a freshwater top predator.

Conditions experienced in early life stages can be an important determinant of individual life histories. In fish, environmental conditions are known to affect early survival and growth, but recent studies have also emphasized maternal effects mediated by size or age. However, the relative sensitivity of the mean fitness (population growth rate λ) to different early life impacts remains largely unexplored. Using a female-based integral projection model (IPM) parameterized from unique long-term demographic data for pike (Esox lucius), we evaluated the relative fitness consequences of different early life impacts, including (i) maternal effects of length on egg weight, potentially affecting offspring (first year) survival, and (ii) effects of temperature on offspring growth and survival. Of the seven vital rates defining the model, offspring survival could not be directly estimated and four scenarios were defined for this rate. Elasticity analyses of the IPM were performed to calculate (i) the total contribution from different lengths to the elasticity of λ to the projection kernel, and (ii) the elasticity of λ to underlying variables of female current length, female offspring length at age 1, and temperature. These elasticities were decomposed into contributions from different vital rates across length. Egg weight increased with female length, as expected, but the effect leveled off for the largest females. However, λ was largely insensitive to this effect, even when egg weight was assumed to have a strong effect on offspring survival. In contrast, λ was sensitive to early temperature conditions through growth and survival. Among mature females, the total elasticity of λ to the projection kernel generally increased with length. The results were robust to a wide range of assumptions. These results suggest that environmental conditions experienced in early life represent a more important driver of mean population growth and fitness of pike than maternal effects of size on offspring survival. We discuss two general mechanisms underlying the weak influence of this maternal effect, suggesting that these may be general for long-lived and highly fecund fishes. This model and results are relevant for the management of long-lived top predators, including many commercially important fish species.

Reproductive consequences of female size in haematophagous ectoparasites.

To test relationships between maternal size, egg size and size of new offspring, we studied (a) the effect of maternal size on egg size and number, and maternal survival after oviposition and (b) the effect of egg size on the duration of development and new imago size in three flea species (Xenopsylla ramesis, Synosternus cleopatrae, Parapulex chephrenis) with varying host and habitat specificity. In general, the number and size of eggs as well as total egg volume appeared to be independent of maternal body size. There was no trade-off between egg number and size. However, female body size was related to post-oviposition survival, with larger females surviving longer after oviposition than smaller females. In addition, females that produced more eggs died faster after oviposition in X. ramesis but not in the two other species. There were no significant size differences between eggs that developed into new imagoes and eggs that did not survive. Survivorship of male and female eggs did not differ; however, new adult females were significantly larger than new adult males. Female, but not male, new imagoes exhibited a significant positive relationship between egg size and duration of preimaginal development in all three species, with larger eggs developing faster than smaller eggs. In X. ramesis and S. cleopatrae, faster developing eggs also developed into larger new imagoes. We conclude that these patterns were largely consistent among the three flea species, suggesting that they result from the same mechanisms and are weakly affected by the ecological specialization of a given species.

Effects of dam size and nutrition during pregnancy on fetal ovarian development of their offspring in sheep

This study examined the effects of maternal size at conception and nutrition during pregnancy on ovarian development in their offspring. Romney ewes were selected at mating for heavy (H) or light (L) live weights and body condition, and then allocated to either ad libitum (A) or pregnancy maintenance (M) nutrition from Days 21–140 of pregnancy, resulting in four treatment groups; HA, HM, LA and LM. Ewes were euthanised on Days 65 (P65), 100 (P100) and 140 (P140) of pregnancy to collect fetal ovarian tissue, which was processed for morphological evaluation and immunohistochemical study of AMH and GDF9 (P140 only). Fetuses from H-dams had more oocytes in the first meiotic prophase on P65 (P=0.05) than those from L-dams. On P100, LA-fetuses had more primordial and fewer primary follicles than did LM-fetuses (P<0.05). On P140, fetuses from M dams had more primordial and fewer primary follicles compared with fetuses from A dams. Also on P140, H–M fetuses had greater (P=0.05) AMH expression than L-M fetuses. These results indicate that maternal size at conception and nutrition during pregnancy exert minor effects on fetal ovarian cell number.

Maternal versus environmental constraints on the oocyte size of a marine pelagophil fish

We investigated maternal body size and environmental effects on the oocyte size of the Atlantic sardine, Sardina pilchardus, a marine pelagophil, using a novel, oocyte stage-specific approach which takes into account the spawning lag. In particular, we focused on anatomical constraints imposed by the maternal body cavity to the growth of the ovary and its oocytes during the course of vitellogenesis (VIT) and oocyte maturation (OM). We analyzed variability in oocyte size in VIT and OM ovaries as a factor of maternal size, ambient temperature (SST) and preservation medium (formalin vs. ethanol) using the spawning lag of recent and imminent spawners, respectively, as a covariate. We showed that oocyte size correlates with maternal size in OM ovaries but not in VIT ovaries. More specifically, 10 cm difference in maternal body length corresponds to 0.112 mm2 (or 12 %) difference in the cross section of fully hydrated oocytes just previous to ovulation. On the other hand there was no inverse relationship between OM oocyte size at spawning and batch fecundity. Ambient SST was not an important determinant of hydrated oocyte size since the same 12 % difference in oocyte size was estimated for the entire SST range of the study. We suggest that these stage-specific differences in the effect of maternal size on oocyte size are due to a functional relationship between the abdominal volume and ovarian size.

Reproductive biology of the Alaska skate Bathyraja parmifera, with comments on an intersexual individual.

A total of 1357 specimens of Alaska skate Bathyraja parmifera were collected in the eastern Bering Sea by fisheries observers and during scientific groundfish surveys from 2003 to 2005. Male and female gonads were examined for maturity stage and seasonal reproductive timing. Based on seasonal reproductive data, including the occurrence of egg cases, ovum size, ovum number, shell-gland width and gonado-somatic index, this species appears to reproduce continually throughout the year. Potential effects of maternal size upon the size and number of mature oocytes were also investigated, with total length having a significant, although weak, influence on both. Morphology of a single intersexual individual encountered during the collection period is also described.

The effect of parental size on spermatophore production, egg quality, fertilization success, and larval characteristics in the Caribbean Spiny lobster, Panulirus argus

AbstractThe average size of spiny lobsters (Decapoda; Palinuridae) has decreased worldwide over the past few decades. Market forces coupled with minimum size limits compel fishers to target the largest individuals. Males are targeted disproportionately as a consequence of sexual dimorphism in spiny lobster size (i.e. males grow larger than females) and because of protections for ovigerous females. Therefore, overexploitation of males has led to sperm limitation in several decapod populations with serious repercussions for reproductive success. In the Caribbean spiny lobster, Panulirus argus, little is known about the effect of reduced male size on fertilization success or the role that individual size plays in gamete and larval quality. We conducted a series of laboratory experiments to test the relationship between male size and spermatophore production over multiple mating events and to determine whether spermatophore reduction and female size affected fertilization success or larval attributes in P. argus in the Florida Keys, FL (USA). We found that over consecutive matings, larger males consistently produced spermatophores of a greater weight and area than smaller males, although size-specific differences in sperm cell density were undetected and probably obscured by high variance in the data. Where spermatophores were experimentally reduced to mimic the decline in spermatophore size with declining male size, fertilization success (the number of fertilized eggs/total number of eggs extruded) declined, indicating that sperm availability is indeed limited. No maternal size effects on egg size or quality (C:N ratio) or larval quality (size, swimming speed, mortality) were observed. Our results demonstrate the importance of maintaining large males in populations of P. argus to ensure fertilization success and caution against their overexploitation through fishing, which may severely reduce reproductive success and thus population sustainability.

Brood ball size but not egg size correlates with maternal size in a dung beetle, Onthophagus atripennis

Contrary to the theoretical prediction that the optimal investment per offspring should be independent of maternal size, maternal size and investment per offspring are often positively correlated. However, some previous studies have reported a weak correlation or no correlation. Thus, it remains unclear why a positive correlation between maternal size and the investment per offspring persists in some organisms contrary to the theoretical prediction. In species in which the parents provide food for their offspring, the main components of parental investment are egg size and provisioning mass. Dung beetle (Onthophagus atripennis Waterhouse) parents produce dung brood balls, each of which is the whole provisioning mass for one offspring to grow to adulthood. Parental body size, egg size, and brood ball size were measured in O. atripennis. No correlation was found between maternal size and egg size, but a positive correlation was found between maternal size and brood ball size. Thus, the effect of maternal size differed between egg size and brood ball size. The positive correlation between maternal size and brood ball size may be a by‐product of the brood ball construction process, because the egg maturation period determines brood ball size. Thus, the brood ball construction process may prevent the beetles from investing their resources optimally. It may often however be an advantage for the beetles because it allows the female to adjust the brood ball size according to variable dung quality.

Variability in rockfish (Sebastes spp.) fecundity: species contrasts, maternal size effects, and spatial differences

Over 60 species of rockfish (Sebastes spp.) reside off the coast of California, many of which are economically important to both recreational and com- mercial fisheries. Rockfish are live-bearers with a di- verse array of reproductive strategies. Understanding thereproductivepotentialofanexploitedstockiscritical to assessing the health and status of a fishery. We inves- tigated the reproductive ecology offour rockfish species to examine species contrasts and to determine spatial and maternal-size effects on reproductive potential. Females were sampled during the winter parturition season (November through March) of 2009 through 2012. Maternal length and somatic weight were posi- tively correlated with relative fecundity (larvae per g somatic weight) in all four species, indicating a dispro- portionately greater reproductive output by larger, older females. Fecundity estimates in Chilipepper, S. goodei, and Yellowtail rockfish, S. flavidus ,v aried regionally, but did not significantlydiffer overtimewithinthe years sampled (sample sizes for Speckled, S. ovalis ,a nd Blackgill rockfish, S. melanostomus, were too small to allow spatiotemporal comparisons). Two reproductive strategies were evident as Yellowtail and Blackgill rockfish produced a relatively highly fecund, single brood of smaller-sized larvae annually, in contrast to Chilipepper and Speckled rockfish, which produced larger-sized larvae with lower fecundity. In some re- gions multiple broods were common, complicating es- timates of annual fecundity for these two species. There was some evidence that egg production was positively correlated with female condition, indicating that envi- ronmental variability in oceanographic conditions and productivity may drive changes in fecundity and repro- ductive strategy (i.e., single versus multiple broods).

Reproductive output traits of the simultaneous hermaphrodite &lt;I&gt;Serranus scriba&lt;/I&gt; in the western Mediterranean

We studied multiple individual parameters that affect the reproductive output in the painted comber Serranus scriba , a simultaneous hermaphroditic fish that is widely exploited by recreational fishing in temperate marine coastal regions. Batch fecundity was significantly affected by maternal size, but was not related to maternal age or condition. However, egg quality as estimated by egg dry weight was significantly influenced by the interaction effect of maternal size and age. An empirical assessment demonstrated the existence of a diel spawning pattern based on a daily release of a partial fraction of eggs related to sunset time. Buoyancy varied during the incubation period, but it consistently resulted in positive buoyancy that situated the eggs near the top of the water column. This study represents the first estimation of reproductive output of the simultaneous hermaphrodites S. scriba and also provides a comprehensive study about the potential maternal factors that affect egg production. These results are a crucial step towards ongoing efforts to improve the stock assessment of this species.

Does maternal size affect red king crab, Paralithodes camtschaticus, embryo and larval quality?

Stock assessment of Alaskan red king crab, Paralithodes camtschaticus (Tilesius, 1815), can be improved by incorporating reproductive output, which requires an understanding of maternal size effects on embryo and larval quality. In June 2009 and 2010, we collected clutches of recently extruded red king crab embryos in Bristol Bay, Alaska, to assess embryo quality based on dry weight, carbon and nitrogen content. To assess larval quality, we collected ovigerous females from Bristol Bay in 2007 and reared them in the laboratory until larval hatching in 2008. Larval quality based on dry weight, carbon and nitrogen content, and times to 50% mortality under starvation conditions were assessed. All samples were collected in years that were colder than the 15-year average in the eastern Bering Sea. Among the measures of embryo quality, only nitrogen content was significantly different, increasing with maternal size. Carbon and nitrogen content were significantly higher for embryos in 2009 than in 2010, suggesting inter-annual differences in maternal investment. No effect of maternal size with larval quality was found. Our results indicate that maternal size does not have a biologically significant effect on embryo and larval quality in colder-than-average years, and therefore maternal size effects on embryo and larval quality does not need to be explicitly incorporated into reproductive output estimates in stock assessments under these conditions. We are, however, cautious to extrapolate our results to years with different environmental conditions. Further study is needed to fully resolve the possible interaction of environment with maternal size effects on embryo and larval quality for red king crab.

Do ewe size and nutrition during pregnancy affect foetus and foetal organ weight in twins?

This study set out to investigate the effects of ewe size and nutrition during pregnancy on the development of twin-foetuses and was part of a large study investigating life-time effect of maternal size and nutrition on the offspring. Heavy (H) and light (L) Romney ewes were allocated to ad libitum (A) or maintenance (M) nutritional regimens from day 21 to day 140 of pregnancy (P21–P140). At P65, P100 and P140, five (total of 59 ewes) twin-bearing ewes from each size-by-nutritional-treatment group were euthanized and foetal organs were collected and weighed. L-ewes were lighter and had greater changes in live weight from breeding to P65, P100 and P140 than H-ewes. M-ewes were lighter and had smaller changes in live weight than A-ewes from breeding to P65, P100 and P140. No ewe-size or nutritional effects were found on organ weights measured at P65. At P100, ewe size and nutritional level had no effect on foetal weight. Foetuses from M-ewes had 7% heavier livers after correcting for foetal weight, compared to those from A-ewes at P100. At P140, foetuses from L- and M-ewes were lighter than foetuses from H- and A-ewes. In addition, foetuses from M-ewes had lighter thyroid glands (34%) but heavier livers (14%) and kidneys (11%) than foetuses from A-ewes after correction for foetal weight. In conclusion, ewe size constrained twin foetuses in late gestation, but not in early or mid gestation. Similarly, maternal nutrition had only few effects on foetal development in early- and mid-pregnancy, however, foetal development was more affected in late gestation, suggesting that the twin-foetuses were nutrient deprived in this late period only.

The conservation and fishery benefits of protecting large pike ( Esox lucius L.) by harvest regulations in recreational fishing

Traditional fisheries management theory supports aggressive exploitation of old and large fish to maximize a stock’s biomass production and yield. Here we present an age-structured fish population model with multidimensional density-dependence to test the hypotheses that protection of large, fecund individuals is beneficial for the population and selected fisheries variables and that effects of maternal size on early survival rate change the resilience and fisheries productivity of a pike population ( Esox lucius L.) exploited by recreational angling. We find that, compared to the traditional regulatory approach of management by small minimum-length limits (so that culling of large fish is encouraged), preservation of large and old individuals through harvestable-slot length limits promises considerable benefits for fisheries quality, without compromising the long-term conservation of the population. We also find that ignoring maternal effects on early survival of offspring might overestimate the equilibrium spawning stock abundance by up to 17% and the predicted harvest by up to 11%, potentially putting pike populations at risk from overharvest if size-dependent maternal effects are ignored in fisheries models. If the findings from our simulation study hold for empirical systems, they suggest altered harvest regulations in many of consumptive pike recreational fisheries are needed to protect large individuals to a greater extent that currently pursued.

MATING, DEVELOPMENT AND EFFECTS OF FEMALE SIZE ON OFFSPRING NUMBER AND SIZE IN THE NEOGASTROPOD BUCCINUM ISAOTAKII (KIRA, 1959)

The copulation, egg laying and embryonic development of the commercially harvested marine neogastropod Buccinum isaotakii (Kira, 1959) were investigated in laboratory‐reared individuals. The effect of maternal size on offspring size and production was examined. Copulation was preceded by aggregations and occurred both by day and night at varying frequencies (1—5 times per female). Duration of copulation ranged between 120 and 375 min per bout. Egg laying commenced approximately 1 month after copulation. Mature B. isaotakii exhibited both communal and individual egg laying. A total of 80 depositions, 65 communal and 15 individual, were recorded. Buccinum isaotakii displays conventional direct development. Hatching occurred between 6 and 7 months after egg masses were laid. Juveniles were released from the capsule through the apertural plug. The head had black pigmentation and a pale yellow shell was present on hatching. Regression analysis showed a significant relationship between both the number of capsules per egg mass and egg mass wet weight and female shell length, but not between egg capsule basal width and height. Female shell length was also correlated with capsule width, length, height and wet weight. Egg capsule width was correlated with the number of eggs, veligers, pediveligers, pre‐hatching juveniles and hatchlings per capsule but not with the sizes of eggs, veligers, pediveligers, pre‐hatching juveniles and hatchlings. The study found that 1.1—2.0% of eggs completed their development.

Incubation environment affects phenotype of naturally incubated green turtle hatchlings

A comparison of body size and flipper size was carried out on green turtle (Chelonia mydas) hatchlings produced from natural nests at two beaches on Ascension Island, South Atlantic and one beach in northern Cyprus in the Mediterranean (N=18 nests; N=180 hatchlings). Hatchlings from Ascension Island were significantly larger and heavier than hatchlings in Cyprus, a likely consequence of maternal size effects. Incubation temperature appeared to influence body size of hatchlings on Ascension Island with higher temperatures producing smaller hatchlings. Both hind and fore-flipper area scaled positively with body size. In proportion to body size, hind-flipper area appears relatively consistent among the Atlantic populations but is smaller than hatchlings measured in Hawaii.

Effects of plant size on reproductive output and offspring performance in the facultative biennial Digitalis purpurea

Summary Monocarpy in facultative biennials can be favoured by selection when there is a more than proportional increase in fitness with size. The possible contributions of larger reproductive output and higher offspring quality to such an increase were investigated in the facultative biennial plant Digitalis purpurea. Straw mass (rosette leaves and flowering stem excluding fruits and seeds) was determined for 100 individuals of varying size and correlated with the number of flowers and seeds per flower to examine whether sex‐allocation is size dependent. To determine whether maternal size influences offspring growth, and whether this effect is more pronounced in the presence of competition, seeds from 32 maternal plants were grown alone, and with one, two or four competitors. Total seed number increased proportionally with size. Seed quality, measured as seed size, germination percentage and speed also increased with maternal size. The combined fitness measures of total seed mass (seed number × seed size), number of seedlings (seed number × germination percentage) and total female fitness (seed number × germination percentage × mean offspring dry mass after 14 weeks) all increased disproportionally with size. Sex‐allocation was size dependent, with large plants emphasizing the female function. Offspring dry mass after both 8 and 14 weeks of growth was strongly influenced by competition, whereas the effect of maternal size was significant only at the first harvest date. Competition did not accentuate the effects of maternal size. The results support that monocarpy exists in D. purpurea because of increased offspring quality rather than a disproportionate advantage in seed output of large individuals.

Postnatal cardiovascular function after manipulation of fetal growth by embryo transfer in the horse.

This study used between-breed embryo transfer in the horse to investigate the effects of maternal size and uterine capacity on fetal growth and postnatal cardiovascular and neuroendocrine functions. Equine embryos were transferred to establish eight Thoroughbred-in-Thoroughbred (TinT), seven Pony-in-Pony (PinP), five Thoroughbred-in-Pony (TinP) and eight Pony-in-Thoroughbred (PinT), pregnancies. Maternal and foal weights and placental microscopic area were measured at birth. At 6 days of postnatal life, arterial blood pressure and heart rate were monitored and blood samples were taken for hormone analysis before, during and after a 10 min period of nitroprusside-induced hypotension. Values for maternal and foal weights and placental area at birth were larger in TinT than in PinP pregnancies (P < 0.05). PinT pregnancies resulted in larger placentae and heavier foals relative to PinP (P < 0.05). TinP had smaller placentae and lighter foals relative to TinT (P < 0.05). Growth-enhanced (PinT) foals showed elevated basal arterial blood pressure and baroreflex threshold, reduced baroreflex sensitivity, diminished plasma catecholamine responses to acute stress, and increased cortisol responsiveness to ACTH. Conversely, growth-restricted (TinP) foals showed no change in basal arterial blood pressure, baroreflex threshold or adrenocortical responsiveness to ACTH, but had enhanced baroreflex sensitivity and augmented plasma catecholamine responses to acute stress. The data show that fetal growth acceleration as well as fetal growth restriction, resulting from between-breed embryo transfer in the horse, leads to altered postnatal regulation of blood pressure and the circulating concentrations of cortisol. These findings suggest that deviations in the pattern and rate of fetal growth both above and below the normal trajectory may influence cardiovascular function in postnatal life.

Lactation, maternal behavior and infant growth in common marmoset monkeys ( Callithrix jacchus ): effects of maternal size and litter size

We examined the relationship between lactation performance and infant growth in a captive population of common marmosets (Callithrix jacchus) that varied in both maternal and litter size. Though common marmosets display a typical primate pattern of dilute milk and relatively slow infant growth rates (factors associated with low daily lactation investment and minimal maternal size effects), we hypothesized that the marmoset's small body size would make lactation investment more sensitive to maternal size than is true for larger-bodied primates. Smaller mothers rearing twins had lower milk fat, lower gross energy in milk samples collected in mid to late lactation and lower nursing-bout frequencies than did large mothers nursing twins. Lactation performance and maternal behavior did not differ between large and small mothers when rearing singletons, with a single exception: small mothers had a lower gross energy in mid-lactation milk samples. Relative growth rates in twins but not singletons were affected by maternal size, such that small mothers supported more growth per infant when rearing singletons while large mothers supported more growth per infant when rearing twins. Among the larger mothers, only, older mothers supported somewhat, though not significantly, less growth per infant, regardless of litter size. Twin infants of small mothers appeared to respond to below-optimal levels of milk yield by initiating maternal carrying less often. The relative energy intake of mothers was similar regardless of litter or maternal size. Small mothers rearing twins drew more heavily on reserves, reflected in a linear weight loss during lactation; however, the reserves drawn upon were inadequate to meet the lactation demand, resulting in lower milk energy output. In addition, small mothers rearing twins were more likely to be ill and less likely to be fertile in the year following lactation than were large mothers of twins or mothers of any size rearing singletons.

The influence of propagule size and maternal nest‐site selection on survival and behaviour of neonate turtles

Summary Maternal effects are widely recognized as important ecological and evolutionary forces, with fitness consequences for both offspring and parents. However, little is known about the impact of maternal effects on the survival and behaviour of offspring in the field. Two potentially important maternal effects that influence the phenotypes and survival of neonates are (i) propagule size effects (i.e. egg size, hatchling size and clutch effects) and (ii) nest‐site selection, which influences incubation conditions and the suitability of habitat for neonates after hatching. We experimentally removed the effects of variable incubation conditions to focus on how propagule size effects and nest‐site microhabitat characteristics influence hatchling survival and behaviour in the Common Snapping Turtle,Chelydra serpentina. Using eight simultaneous experimental releases of neonates under ecologically relevant field conditions, we detected no influence of propagule size effects on hatchling turtle survival or behaviour. Egg mass, hatchling mass, hatchling carapace length and clutch did not predict the probability of survival, nor did they influence hatchling behaviour. However, nest‐site microhabitat characteristics were important for both survival and behaviour. The probability of hatchling survival increased with decreasing amounts of ground vegetation and slope at the release point. Hatchlings took longer to reach the fence when released in areas with more ground vegetation and dispersed farther when released from greater distances and at lower slopes. Therefore, variation in maternal behaviour, such as nest‐site selection, is an important effect because it results in differential survival and behaviour of offspring in this population, whereas variation in maternal size effects alone does not.

Factors Influencing Fetal Growth

After completing this article, readers should be able to: 1. Describe the roles of insulin-like growth factor on fetal growth and development. 2. Delineate components of “maternal constraint.” 3. Explain the role of the placenta in regulating fetal growth. 4. Describe the effects of fetal glucose, amino acid, and fat supply on fetal growth. The principal determinants of fetal growth are fetal genotype and in utero environment. Environmental factors include maternal and paternal genetics, maternal size, and the capacity of the placenta to provide nutrients to the fetus. These environmental factors interact with the intrinsic growth pattern of the fetus, yielding a particular rate and composition of fetal growth. Most of the variation in fetal growth in a population is due to variations in environmental factors, not the fetal genome, although a genetically abnormal fetus clearly might not grow as well as a normal fetus if affected genes include those that are important for growth. Many genes contribute to fetal growth and birthweight. Techniques in which specific genes can either be deleted (“knockouts”) or overexpressed have led to greater understanding of how some of these genes regulate fetal growth. Such studies have shown that both maternal and paternal influences are present during fetal development and are passed on to the developing fetus by spermatozoa or oogonia by a mechanism called imprinting. Although the maternal genetic composition exerts greater influence than fetal genotype in the overall regulation of fetal growth, both maternal and paternal genomes are important in fetal growth and development (1)(2). For example, gynogenetic zygotes (two maternal genome copies) lead to underdeveloped extraembryonic tissues but well-developed embryos. The more modest regulation offered by the paternal genotype is essential for trophoblast development. For example, zygote nuclear transfer experiments have shown that androgenetic zygotes (two paternal genome copies) develop extensive trophoblast tissues but …