A review of maternal and embryonic control of phase-dependent progeny characteristics in the desert locust

Hatchlings of the desert locust, Schistocerca gregaria, display phase polyphenism in body coloration and size. This phenomenon has been found to be maternally controlled and two different mechanisms have been proposed to explain the underlying process. One mechanism claims that a water-soluble pheromonal factor secreted by gregarious female adults into the foam plugs of egg pods induces darkening in their progeny. The other mechanism states that hatchling body coloration is pre-determined in the ovaries and that no foam factor is involved in this phenomenon. This mechanism was supported by the observation that hatchling melanization was not prevented by the early washing or separation of eggs, which should have removed the pheromonal factor from the eggs and produced green hatchlings according to the other mechanism. This paper reviews the latest findings related to this phenomenon with special reference to reproductive cycles and genetic differences. The close relationships between egg size and the degree of melanization in hatchlings may provide strong evidence against the possible involvement of the pheromonal factor, because egg size is determined in the ovarioles. Furthermore, the absence of “solitarizing” effects of early washing and separation on hatchling melanization was also confirmed in different genetic strains. A hypothesis proposed by others that such effects occur only in eggs from the first reproductive cycle was tested and rejected. Based on these and other results, a model to explain the mechanisms underlying the maternal control of progeny characteristics and embryonic control of melanization in the hatchling was proposed.     

Maternal effects on progeny body size and color in the desert locust, Schistocerca gregaria: examination of a current view

Hatchling body color and size of the desert locust, Schistocerca gregaria, are determined by the population density of the mothers during their reproductive period. Smaller green hatchlings are produced by adults at low population density (solitarious conditions) and larger dark hatchlings at high population density (gregarious conditions). One claim states that a pheromonal factor secreted by gregarious mothers into foam plugs of egg pods induces darkening in hatchlings. Previous research suggests that the foam factor can be removed by separating eggs individually within 1h of deposition, causing presumptive gregarious eggs to hatch without darkening. The present study re-examined this claim and possible factors that have been proposed which could account for the difference between our results and those reported earlier. Early separation was performed on eggs with a low mortality rate. The results showed that the egg separation did not increase the incidence of green hatchlings. Once chorionated in the ovary, eggs remained unchanged in size until the second day after oviposition in either isolated or crowded locusts. This and other results suggest that the phase-dependent differences in body size and color of hatchlings are established in the ovary and that modifications by the accessory gland factor either in the oviduct or after deposition are unlikely.     

Artificial miniaturization causes eggs laid by crowd-reared (gregarious) desert locusts to produce green (solitarious) offspring in the desert locust, Schistocerca gregaria

The mechanism underlying the phase-dependent polyphenism in hatchling body coloration was studied by testing for a possible causal relationship with egg size in the desert locust, Schistocerca gregaria. Crowd-reared (gregarious) females typically produce large, black offspring, whereas females reared in isolation (solitarious) deposit small, green offspring. We first tested for possible genetic differences in the role of egg foam by washing or separating eggs from two strains of locust. No solitarizing effect was found in either of the strains tested, supporting a previous finding, using another laboratory strain, to show that the hatchling body coloration and size are pre-determined in the ovary of the mother and no egg foam factor is involved in the control of the hatchling body coloration. Topical application of fenoxycarb, a juvenile hormone analog (JHA), and implantation of extra corpora allata (CA), taken from Locusta migratoria, caused gregarious female adults of S. gregaria to produce small eggs. Some eggs laid by CA-implanted females produced green hatchlings. All large eggs chosen among those deposited by gregarious females produced black hatchlings. When eggs were either kept on dry filter paper at nearly saturated relative humidity during embryogenesis or pricked with a needle so that some egg yolk was squeezed out, some produced small, green hatchlings. These results suggested that the amount of egg yolk or the availability of yolk material may determine the body coloration of hatchlings.     

The role of egg pod foam and rearing conditions of the phase state of the Asian migratory locust Locusta migratoria migratoria (Orthoptera, Acrididae)

Coloration phase state, morphometrical ratios and the numbers of mature oocytes of Locusta migratoria migratoria were examined in a series of experiments to determine the means by which phase characteristics are passed to the next generation. Washing with distilled water of eggs from egg pods laid by gregarious crowd-reared females resulted in solitarization of the hatchlings after their isolation, indicating that a factor present in eggs encapsulated in foam is causal to gregarization. Such locusts showed a significant shift towards the typical solitarious body coloration, morphometry and number of mature oocytes as compared to locusts resulting from unwashed eggs. Gregarious coloration, morphometrical ratios and oocyte numbers could be partially restored when hatchlings from washed eggs were regrouped. When gregarious locusts were reared in isolation, they showed a solitary body color, whereas, morphometry and oocyte numbers were not affected by isolation.     

孵化温度对王锦蛇胚胎代谢和幼体适合度的影响

孵化温度所驱动的爬行动物的表型变异是生理生态学研究的热点。本研究以王锦蛇(Elaphe carinata)为实验动物,检验了24℃和28℃孵化温度对王锦蛇胚胎代谢速率、孵化过程中的卵重量、孵出幼体代谢和行为的影响。研究结果显示:卵重和胚胎的呼吸代谢均与孵化时间呈正相关;28℃下胚胎代谢速率大于24℃;幼蛇孵出15 d内体重随着生长时间的延长而减小,24℃孵出幼体的代谢速率大于28℃孵出幼体,两温度下孵出幼体的呼吸代谢速率和生长时间无显著关系;28℃孵出幼体的疾游速和吐信频次均大于24℃;两孵化温度孵出幼体的选择体温无显著差异,但在消耗完体内的剩余卵黄后28℃孵出幼体有60%的个体摄食,而24℃孵出幼体无摄食个体。总体而言,王锦蛇28℃孵出幼体适合度优于24℃孵出幼体。     

Effects of hatchling body colour and rearing density on body colouration in last-stadium nymphs of the desert locust, Schistocerca gregaria

Abstract.  The influences of hatchling character and rearing density on body colour at the last-nymphal stadium are investigated for the desert locust, Schistocerca gregaria . Hatchlings are divided into five groups based on the darkness of the body colour and reared either under isolated or crowded conditions. Two types of body colour variation at the last-nymphal stadium are separately analysed (i.e. the background colour and black patterns). Under isolated conditions, the background body colour is either greenish or brownish. Most individuals are greenish and the highest percentage of brownish insects is obtained from hatchlings with the darkest body colour. Under crowded conditions, the background colour is yellow or orange and the percentage of yellowish nymphs tends to decrease when they are darker at hatching. The intensity of black patterns differs depending on the body colour at hatching and subsequent rearing density. Most isolated-reared nymphs exhibit few or no black patterns but nymphs with some black patterns also appear, particularly among those that had been dark at hatching. Under crowded conditions, the black patterns become more intense when they are darker at hatching. Therefore, last-stadium nymphs with typical solitarious or gregarious body colouration appear when they have the phase-specific body colouration at hatching as well. The present results demonstrate that both body colour at hatching and rearing density during nymphal development influence body colouration at the last-nymphal stadium.     

The role of female accessory glands in maternal inheritance of phase in the desert locust Schistocerca gregaria

Accessory glands of crowd-reared females of Schistocerca gregaria were ligatured from the lateral oviducts. Hatchlings resulting from egg pods laid after the treatment showed a significant shift towards solitarious behaviour as compared to hatchlings from control-treated females. Morphometric measurement of hatchlings revealed no consistent difference between ligatured and control females, however, one ratio (hind femur length/vertex width) was approaching significance. Hatchlings from eggs of crowd-reared females behaved solitariously when freshly laid eggs were washed with a saline solution. Gregarious behaviour could be restored when washed eggs were treated with a saline extract of the accessory glands. The colouration of hatchlings was not affected by any treatment. Our findings implicate the accessory glands in the production, release or activation of the recently reported gregarizing factor found in the egg pod foam [McCaffery, A.R., Simpson, S.J., Islam, M.S., Roessingh, P., 1998. A gregarizing factor present in the egg pod foam of the desert locust Schistocerca gregaria. Journal of Experimental Biology 201, 347-363].     

Erfahrungsbericht über die Haltung und deutsche Erstzucht der Borneo-Flussschildkröte (Orlitia borneensis Gray, 1873) im Zoo Dresden

Dresden Zoo bred successfully the Malaysian giant turtle (Orlitia borneensis) in summer 2012. This was the first successful breeding of this species in Germany.Little is known about biology and behaviour of this large river turtle and keeping and especially breeding of this endangered species in captivity is a rarity. In order to create optimal breeding conditions Dresden Zoo rebuilt an enclosure for the turtles in 2010. An area with soil and sand was built for the expected egg deposition. After arranged matings one female dug a nest on this area and buried her eggs. Nine eggs were secured and transferred into an incubator in a box filled with a 1:1 mixture of vermiculite and water. The average temperature was 29 °C. After problems with the temperature regulation the damaged incubator had to be replaced. Because of an estimated incubation period of 3–4 months, one egg was opened on day 127 of incubation. A live hatchling with a big yolk sac was fetched. Because of the non-reabsorbed yolk sac the hatchling was further incubated. On day 154 of incubation all eggs were manually opened and the hatchlings were fetched. All of these hatchlings showed a non-reabsorbed yolk sac and were incubated onwards in a box with wet paper towel until the yolk sac was completely reabsorbed. After that the hatchlings were housed solitarily in a box with water of approximately 4 cm height and a small land area. Two days after housing food was offered for the first time. All hatchlings accepted the offered food consisting of herbal as well as of animal products and later turtle pellets and self-made turtle jelly.Though little is known about breeding this species, the breeding success of Dresden Zoo demonstrates a possible approach to this topic. But there are still things to optimize. For example the manual hatching is something that should be avoided in future. Fertilization and hatching rate of 100% are promising and up to date eight out of nine hatchlings are still alive.     

Epigenetic transmission of phase in the desert locust, Schistocerca gregaria: Determining the stage sensitive to crowding for the maternal determination of progeny characteristics

Desert locust female adults respond to crowded conditions by changing progeny characteristics such as egg size, clutch size (no. of eggs per pod), hatchling body size and coloration. This study was conducted to determine the stage sensitive to crowding in this locust. Reproductively active females reared in isolation increased egg size and decreased clutch size and the proportion of green hatchlings after exposure to crowded conditions (in which each female was kept with four male adults). These changes depended not only on the timing of exposure to crowded conditions during the reproductive cycle but also on the length of the exposure. By varying the time and length of the exposure, it was found that crowding had no influence on progeny characteristics during the last two days of egg development at 31 °C and that there was a four-day sensitive stage before this period. The sensitive stage coincided with the time when the affected oocytes were 1.5-4 mm long, while the sensitivity to crowding appeared to be constant over the sensitive stage. The larger the magnitude of the increase in egg size after exposure to crowding, the smaller the proportion of green hatchlings (and the larger the proportion of gregarized dark hatchlings); there was a sigmoidal relationship between the two variables. Based on these results, we propose a model for determining the stage sensitive to crowding in both the female parent and the oocytes.     

Nonlinear continuum of egg size-number trade-offs in a snake: is egg-size variation fitness related?

The relationship between offspring size and offspring number is crucial to life history evolution. To examine how these two life history variables are coupled and whether an altered balance between them will result in changes in maternal fitness, we manipulated clutch size of the Chinese cobra (Naja atra) by using the techniques of hormonal manipulation and follicle ablation. Females receiving exogenous follicle-stimulating hormone produced more but smaller eggs, and females undergoing follicle ablation produced fewer but larger eggs. Neither body size (body mass and snout-vent length) at hatching nor egg mass at oviposition had a role in determining hatchling survival and growth. Female hatchlings were more likely to die in early post-hatching days and grew more slowly than male hatchlings. Our data show that: (1) there is a nonlinear continuum of egg size-number trade-offs in N. atra within which there is a single inflexion where the rate at which egg size decreases with increasing clutch size, or clutch size increases with decreasing egg size, is maximized; (2) there is a fixed upper limit to egg size for a given-sized female, and the limit is not determined by her body volume; (3) egg size has no role in determining hatchling survival and growth; and (4) the extent to which females may enjoy reproductive benefits in a given reproductive episode depends on how well egg size and egg number are balanced.     

How to hatch from an egg of great structural strength. A study of the Common Cuckoo

Brood parasitism represents a unique mode of avian reproduction that requires a number of adaptations. For example, to reduce chances of puncture ejection of their eggs by small hosts, brood parasites may have been selected for laying eggs of unusually great structural strength. However, great structural strength of eggshells should hinder hatching. The goals of our study were to establish if chicks of the Common Cuckoo Cuculus canorus have more difficulty with hatching out of their strong eggs than chicks of species with eggs of similar size, and whether they possess any mechanisms facilitating hatching. To achieve these goals, we compared hatching pattern and selected body characteristics of chicks of the Common Cuckoo with those of another altricial species with eggs of a similar size, the Great Reed Warbler Acrocephalus arundinaceus . Although the rate of pecking was similar in the two species, the Common Cuckoo chicks started pecking earlier in relation to their emergence and consequently required more time and a greater cumulative number of pecks for breaking open their eggs than did young Great Reed Warblers. The two species also differed with respect to the pattern of opening their shells; in contrast to the warbler chicks, which enlarged the original pip circularly, the cuckoo chicks opened the egg by systematically creating a long narrow slit until they emerged. Finally, our study of hatched young revealed several differences; the Cuckoo hatchlings were significantly heavier, had a longer forearm, and their egg tooth was located significantly farther from the tip of the beak. The edge used for cutting through the shell was also significantly longer than that of hatchling Great Reed Warblers. To conclude, our data suggest that hatching is more difficult for a Cuckoo than for a Great Reed Warbler and that Cuckoos possess several mechanisms to overcome the problems of hatching from a structurally strong egg.     

Do temperature fluctuations during incubation always play an important role in shaping the phenotype of hatchling reptiles?

Fluctuating temperatures (FTs) influence hatchling phenotypes differently from constant temperatures (CTs) in some reptiles, but not in others. This inconsistency raises a question of whether thermal fluctuations during incubation always play an important role in shaping the phenotype of hatchlings. To answer this question, we incubated eggs of Naja atra under one CT (28 °C, CT), two temperature-shift [cold first (CF) and hot first (HF) in which eggs were first incubated at 24 or 32 °C and then at the other, each for 20 days, and finally at 28 °C until hatching], and one FT thermal regimes. Female hatchlings were larger in snout–vent length but smaller in tail length, head size than male hatchlings from the same-sized egg; female hatchlings had more ventral scales than did male hatchlings. The FT and HF treatments resulted in shorter incubation lengths. Tail length was greatest in the CT treatment and smallest in the FT treatment, with the CF and HF treatments in between; head width was greater in the CT treatment than in the other three treatments. Other examined hatchling traits did not differ among treatments. The observed morphological modifications cannot be attributed to the effect of thermal fluctuations but to the effect of temperatures close to the upper and lower viable limits for the species. Our results therefore support the hypothesis that hatchling phenotype is not altered by thermal fluctuation in species with no phenotypic response to incubation temperature within some thresholds.     

The effect of egg mass on the growth and survival of blackbirds: a field experiment

A number of studies on birds have shown a positive correlation between egg mass and the growth (or survival) of chicks. However, a correlation based on non-experimental data does not demonstrate that egg mass affects growth, because it could be confounded by parental or territory quality. One way to see if pre-hatching attributes affect growth or survival is to swap hatchlings between nests, so that parental or territory quality do not confound correlations. I conducted such a fostering experiment on the blackbird, Turdus merula . Apart from very light eggs, that did not hatch, egg mass did not affect hatching success. Heavier eggs produced both heavier and larger nestlings. Nestlings raised by their own parents showed a positive correlation between hatchling mass and mass and size both early (day-4) and late (day-8) in the nestling period. The mass and size of fostered nestlings correlated with the mean mass of their natural parents' hatchlings, with higher coefficients early rather than late in the nestling period. By contrast, early in the nestling period there were no significant correlations of nestling mass or size and mean hatchling mass of the foster parents, but there were significant correlations late in the nestling period. Thus pre-hatching attributes of the egg do affect nestling size but environmental effects, including parental or territory quality, have an affect late in the nestling period. Direct manipulations of components of egg mass are required before one can conclude that egg mass affects growth, rather than some correlated pre-hatching attribute. There was no clear effect of egg mass on the probability that a hatching bird would survive until two weeks after fledging (shortly before nutritional independence), despite the fact that nestling mass does correlate with fledgling survival. I suggest that egg mass affects the 'size' component of mass and that juvenile survival depends on the 'condition' component of mass.     

Phase-specific responses to different qualities of food in the desert locust, Schistocerca gregaria: developmental, morphological and reproductive characteristics

Solitarious female adults are known to produce smaller hatchlings than those produced by gregarious adults of the desert locust, Schistocerca gregaria. This study investigated developmental, morphological and reproductive responses to different qualities of food in hatchlings of different phases. Mortality was higher, the duration of nymphal development longer and adult body weight lighter with a low-quality food than a high-quality food. Gregarious hatchlings showed better survivorship, grew faster and became larger adults than did solitarious ones. The incidence of locusts exhibiting extra molting, which was typically observed in the solitarious phase, was dramatically increased when a low-quality food was given to the solitarious hatchlings. Low-quality food caused locusts to shift morphometric ratios toward the values typical of gregarious forms; smaller F/C (hind femur length/maximum head width) and larger E/F (elytra length/hind femur length). Solitarious hatchlings grown at either high- or low-quality foods and then given high-quality food after adult emergence revealed that food qualities during the nymphal stage influence their progeny quality and quantity via adult body size that influenced reproductive performance. Female adults showed an overshooting response to a shift from low- to high-quality food by increasing egg production that was specific to body size. This study may suggest that gregarious hatchlings are better adapted to adverse food conditions than solitarious counterparts and extra molting is induced even among gregarious hatchlings under poor food conditions.     

The effects of thermal and hydric environments on hatching success, embryonic use of energy and hatchling traits in a colubrid snake, Elaphe carinata.

We examined the effects of thermal and hydric environments on hatching success, the embryonic use of energy and hatchling traits in a colubrid snake, Elaphe carinata. The eggs were incubated at four temperatures ranging from 24 to 32 degrees C on substrates with water potentials of 0 and -220 kPa using a 4x2 factorial design. Both thermal and hydric environments affected the water exchange between eggs and their surroundings. Eggs incubated in wetter substrates gained mass throughout the course of incubation, whereas eggs in drier substrates gained mass during the first half of incubation and lost mass thereafter. Hatching success was noticeably higher at 26 and 30 degrees C than at 24 and 32 degrees C, but among treatments, differences in hatching success were not significant. Temperature significantly affected the duration of incubation and most hatchling traits examined. Deformed hatchlings were found in all temperature treatments, with more deformities observed at 32 degrees C. Hatchlings from eggs incubated at different temperatures differed in wet body mass, but the differences stemmed mainly from variation in water contents. Embryos at different temperatures completed development at nearly the same expenditure of energy and catabolized nearly the same amount of lipids, but hatchlings from different temperatures differed in the development condition of carcass at hatching. Hatchlings from eggs incubated at 26 degrees C were larger in SVL than those from other higher or lower incubation temperatures, characteristically having larger carcasses; hatchlings from 32 degrees C eggs were smaller in SVL and had smaller carcasses but larger residual yolks than those from lower incubation temperatures. Hatchlings from eggs incubated at 24 degrees C were shorter in tail length but greater in size (SVL)-specific body wet mass than those from higher incubation temperatures. Within the range from -220 to 0 kPa, the substrate water potential did not affect hatching success, the embryonic use of energy and all hatchling traits examined, and the effects of temperature were independent of the effects of substrate water potential. Therefore, our data add evidence showing that embryonic development in reptiles with pliable-shelled eggs is relatively insensitive to variation in hydric environments during incubation.     

Phenotypic responses of hatchlings to constant versus fluctuating incubation temperatures in the multi-banded krait, Bungarus multicintus (Elapidae)

Most studies on egg incubation in reptiles have relied on constant temperature incubation in the laboratory rather than on simulations of thermal regimes in natural nests. The thermal effects on embryos in constant-temperature studies often do not realistically reflect what occurs in nature. Recent studies have increasingly recognized the importance of simulating natural nest temperatures rather than applying constant-temperature regimes. We incubated Bungarus multicintus eggs under three constant and one fluctuating-temperature regimes to evaluate the effects of constant versus fluctuating incubation temperatures on hatching success and hatchling phenotypes. Hatching success did not differ among the four treatments, and incubation temperature did not affect the sexual phenotype of hatchlings. Incubation length decreased as incubation temperature increased, but eggs incubated at fluctuating temperatures did not differ from eggs incubated at constant temperatures with approximately the same mean in incubation length. Of the hatchling phenotypes examined, residual yolk, fat bodies and locomotor performance were more likely affected by incubation temperature. The maximal locomotor speed was fastest in the fluctuating-temperature and 30 degrees C treatments and slowest in the 24 degrees C treatment, with the 27 degrees C treatment in between. The maximal locomotor length was longest in the fluctuating-temperature treatment and shortest in the 24 degrees C and 27 degrees C treatments, with the 30 degrees C treatment in between. Our results show that fluctuating incubation temperatures do not influence hatching success and hatchling size and morphology any differently than constant temperatures with approximately the same mean, but have a positive effect on locomotor performance of hatchlings.     

The trans-generational phase accumulation in the desert locust: Morphometric changes and extra molting

To understand the underlying trans-generational phase accumulation, a classical morphometric characteristic, the F/C ratio (F, hind femur length; C, maximum head width), of adult desert locusts (Schistocerca gregaria) was monitored over eight consecutive generations. Adult F/C ratios, which are larger in solitarious locusts than in gregarious ones, were negatively correlated to the darkness of body color at hatching. Two successive generations were required for a complete shift from the gregarious (crowd-reared) to the solitarious (isolated-reared) phase and vice versa in the laboratory. That is (1) female adults needed to be exposed to crowded (or isolated) conditions so that their hatchlings would become large (or small) and dark (or green) in color, and (2) the hatchlings then needed to be exposed to crowded (or isolated) conditions for their entire nymphal stage. Solitarious locusts exhibited extra molting that influenced the F/C ratio in the adult stage, but did not exert significant influences on the trans-generational changes in this trait because the incidence was low. The incidence of extra molting was negatively correlated with nymphal survival rates. The morphometric trans-generational changes may be explained without assuming any accumulating internal factor.     

Gold climates and the evolution of viviparity in reptiles: cold incubation temperatures produce poor-quality offspring in the lizard, Sceloporus virgatus

Evolutionary origins of viviparity among the squamate reptiles are strongly associated with cold climates, and cold environmental temperatures are thought to be an important selective force behind the transition from egg-laying to live-bearing. In particular, the low nest temperatures associated with cold climate habitats are thought to be detrimental to the developing embryos or hatchlings of oviparous squamates, providing a selective advantage for the retention of developing eggs in utero, where the mother can provide warmer incubation temperatures for her eggs (by actively thermoregulating) than they would experience in a nest. However, it is not entirely clear what detrimental effects cold incubation temperatures may have on eggs and hatchlings, and what role these effects may play in favouring the evolution of viviparity. Previous workers have suggested that viviparity may be favoured in cold climates because cold incubation temperatures slow cmbryogenesis and delay hatching of the eggs, or because cold nest temperatures are lethal to developing eggs and reduce hatching success. However, incubation temperature has also been shown to have other, potentially long-term, effects on hatchling phcnotypcs, suggesting that cold climates may favour viviparity because cold incubation temperatures produce offspring of poor quality or low fitness. We experimentally incubated eggs of the oviparous phrynosomatid lizard, Sceloporus virgatus, at temperatures simulating nests in a warm (low elevation) habitat, as is typical for this species, and nests in a colder (high elevation) habitat, to determine the effects of cold incubation temperatures on embryonic development and hatchling phenotypes. Incubation at cold nest temperatures slowed embryonic development and reduced hatching success, but also affected many aspects of the hatchlings' phenotypes. Overall, the directions of these plastic responses indicated that cold-incubated hatchlings did indeed exhibit poorer quality phenotypes; they were smaller at hatching (in body length) and at 20 days of age (in length and mass), grew more slowly (in length and mass), had lower survival rates, and showed greater fluctuating asymmetry than their conspecifics that were incubated at warmer temperatures. Our findings suggest that cold nest temperatures are detrimental to S. virgatus, by delaying hatching of their eggs, reducing their hatching success, and by producing poorer quality offspring. These negative effects would likely provide a selective advantage for any mechanism through which these lizards could maintain warmer incubation temperatures in cold climates, including the evolution of prolonged egg retention and viviparity.     

Factors influencing the embryonic development and hatchling size of the oceanic squid Illex coindetii following in vitro fertilization

Egg masses of oceanic squid accidently collected in the wild have been observed only from a few spawning events in aquaria, and as a consequence, the study of their embryos and hatchlings is very limited. Here, we used in vitro fertilization techniques to understand the abiotic factors that influenced egg development and hatchling performance of the ommastrephid squid Illex coindetii from the Mediterranean Sea. Egg and hatchling sizes of these ommastrephids are close to the minimum for cephalopod species, and therefore, short embryonic developmental periods were expected under a Mediterranean temperature regime. Low incubation densities and the use of antibiotics in the incubation medium resulted in relatively high survival rates to hatchling. Hatching time was inversely proportional to incubation temperature and ranged from 5 to 11 days at 21 °C and 13 °C, respectively. The addition of oviducal jelly to the eggs immediately after fertilization, followed by another addition at the beginning of organogenesis, resulted in better chorionic expansion, with an increase in egg diameter, delayed hatching and higher hatchling weight, which suggests a better use of yolk reserves. Larger hatchlings in length and weight also tended to be produced at low temperature, probably also due to better yolk absorption. As this species spawns all year round, size differences between summer and winter hatchlings may be suspected. In vitro fertilization techniques used in the laboratory proved to be useful in shedding some light on the early life of this oceanic squid. Further research is needed to elaborate on tests to predict gamete quality and to develop methods to avoid premature hatching.     

两种麻蜥卵和孵出幼体的特征

研究了山地麻蜥和丽斑麻蜥实验条件下的卵及孵出幼体的特征.山地麻蜥产卵雌体的体长大于丽斑麻蜥,窝卵重小于丽斑麻蜥,但平均卵重和相对窝卵重与丽斑麻蜥相似.两种蜥蜴均通过增加卵长径和卵短径来增加卵重,但卵的外形不同,山地麻蜥卵较长.两种蜥蜴卵孵化过程中均吸水增重.相似孵化条件(波动温度、-12 kPa)下,山地麻蜥的孵化期明显比丽斑麻蜥长.山地麻蜥幼体的尾、头部大于丽斑麻蜥,但体重和SVL相似.