Invariant Clutch Size Research Articles

Intensive and efficient egg-laying tempo of the parthenogenesis mourning gecko Lepidodactylus lugubris

Although suffered from many evolutionary disadvantages, asexual species benefit from their high efficiency to build clonal populations in a novel habitat. Here we report that a parthenogenetic mourning gecko Lepidodactylus lugubris continuously laid 12 clutches within two years. The egg-laying period lasted from mid-April to late October, and the egg-laying interval ranged between 24 and 73 days with a mean of 34.4 days. Referring to this fecundity, a female gecko could reproduce up to 24 clonal female offspring every year, and expand the population size in an efficient way much faster than most bisexual species. The intensive and efficient egg-laying tempo, associated with the parthenogenetic breeding mode, are crucial factors which facilitated their successful colonisation into many islands. Keywords: clonal population, cost of sex, invariant clutch size, invasive species

Long-term monitoring reveals invariant clutch size and unequal reproductive costs between sexes in a subtropical lacertid lizard

Based on 20,000 records representing c. 11,000 individuals from an 8-year capture-mark-recapture (CMR) study, we tested and confirmed a new case of invariant clutch size (ICS) in a sexually dichromatic lacertid lizard, Takydromus viridipunctatus. In the grassland habitat of the early succession stage, females showed strictly low and invariant clutch size, multiple clutches in a breeding season, high reproductive potential, and annual breeding cycles that correspond to the emergence of male courtship coloration. The hatchlings mature quickly, and join the adult cohort for breeding within a few months, whereas adults show low survival rates and a short lifespan, such that most die within one year. Mortality increased in both sexes during the breeding season, especially in females, indicating an unequal cost of reproduction in survival. These life history characters may be explained by two non-exclusive hypotheses of ICS—arboreal hypothesis and predation hypothesis—within the ecological context of their habitat. Our study highlights a confirmed case of ICS, which adapts well to this r-selected grassland habitat that experiences seasonal fluctuation and frequent disturbance.

Overlap of Female Reproductive Cycles Explains Shortened Interclutch Interval in a Lizard with Invariant Clutch Size (Squamata: Gekkonidae:Paroedura picta)

Variable clutch size is unambiguously an ancestral state in reptiles. Only several lizard lineages have evolved so-called invariant clutch size, where all females lay just one or two eggs per clutch. This mode of reproduction is characteristic for geckos. In some gecko lineages, decreased fecundity in a single clutch is compensated by conspicuous shortening of interclutch intervals. The proximate mechanism of high clutch frequency in these geckos is not known. Here, we document that three subsequently laid clutches develop simultaneously in females of the Madagascar ground gecko (Paroedura picta). The extremely short interclutch intervals in this species-even as short as a week-thus could be attributed to the overlap of female reproductive cycles. Such overlap should be associated with altered female hormonal cycles. Based on measurements of hormonal levels, we suggest that cycles of estradiol and progesterone during reproductive cycles of females in P. picta are largely independent. Thus, in contrast to the presumable ancestral reptile state, higher levels of progesterone do not seem to interfere with vitellogenesis in this species. We discuss potential consequences of this derived mode of reproduction, such as possible simultaneous maternal transfer of nutrients and other yolk components to several subsequent clutches.

First grow, then breed and finally get fat: hierarchical allocation to life‐history traits in a lizard with invariant clutch size

Summary 1 Organisms frequently encounter environments with different productivity. Fitness of an individual then depends on decisions made concerning energy allocation to particular life-history traits in a given environment. In reptiles and other ectotherms, individuals on a poor diet commonly reach smaller size and invest less in reproduction, but they often produce larger eggs than well-fed individuals. 2 Several lineages of reptiles including geckos have evolved an invariant clutch size as a derived mode of reproduction. Gecko females produce maximally two large eggs per clutch, but clutches are unusually frequent. Therefore, geckos serve as an interesting group for studying the generality of nutrition-dependent plasticity in life-history. 3 In a laboratory experiment, we manipulated diet in adult females of the Madagascar ground gecko Paroedura picta. Both food-limited and well-fed females followed the same growth trajectory in body and head length. In contrast, allocation to reproduction was highly nutrition-dependent. Although females in both treatment groups reproduced, food-limited females compromised both quantity and quality of their progeny: they laid clutches of smaller eggs in longer intervals. Fat storage was formed only in well-fed females. 4 We propose that the results are best explained by the consecutive hierarchical allocation of resources to growth, reproduction and storage, and discuss the consequences for investigation of life-history trade-offs.

Reproductive ecology of the Kandyan Day Gecko, <i>Cnemaspis kandiana</i>, in Gannoruwa Forest Reserve

Breeding habitats and environmental conditions preferred by Cnemaspis kandiana, its oviposition and reproduction aspects, its interactions with other species in the nesting habitat, and the mode of oviposition were investigated at the Gannoruwa Forest Reserve, Sri Lanka, during fortnightly field surveys from June 2005 to January 2006. Eleven egg clusters in five caves at Gannoruwa were sampled and data on the environmental conditions inside the caves, number of hatched and unhatched eggs, hatchlings, adults and other faunal species in the nesting habitat recorded. Six eggs were incubated in the laboratory. At the nesting sites, ambient temperature varied from 23-30 oC and light intensity from 0-350 lux. The eggs were predominantly laid as pairs (on 85% occasions) suggesting that C. kandiana has invariant clutch size. The hatched and unhatched eggs at each location varied from 1 to over 100, though the maximum number of unhatched developing eggs found at a given time was 18, i.e., a cluster size to vary from 1-18 eggs. Eggs tend to hatch in pairs, after an apparent incubation period of 39-58 days. The hatchlings had a total length of 23.5-25.8 mm. No interaction with regard to reproduction was found between C. kandiana and any other animals at the breeding sites. The egg-laying in this species is probably a combined effect of site fidelity of a female and communal nesting. This might be due to relative scarcity of preferred habitats in the study area.

Clutch size determination in shorebirds: revisiting incubation limitation in the pied avocet (Recurvirostra avosetta)

1. Traits strongly related to fitness, such as offspring number, are expected to show intraspecific variation among individuals. However, offspring number is invariant in several reptiles, birds, and mammals. Most shorebirds (210+ species), for example, have an invariant clutch size of four eggs, which is unexpected in such an ecologically, behaviourally and socially diverse group. 2. The incubation-limitation hypothesis (ILH) suggests that shorebird clutch size is limited by the inability of adults to incubate clutches larger than four eggs. Several recent studies reported no overall costs of incubating experimentally enlarged clutches and concluded no support for the traditional ILH. However, most studies have not measured all potential costs, and none has quantified costs beyond egg hatching. We conducted a clutch-enlargement experiment and measured potential costs both during incubation and chick rearing in pied avocets (Recurvirostra avosetta L.). 3. Hatching was more asynchronous and egg hatchability was marginally lower in enlarged clutches than in controls. Nonetheless, more young hatched from enlarged clutches (mean: 4.2 +/- 0.17 SE) than from controls (3.4 +/- 0.09), and the two groups did not differ in incubation period, complete or partial clutch failure, or hatchling body size, apparently refuting the ILH. 4. However, pairs incubating enlarged clutches occupied poorer feeding territories during chick rearing, experienced higher chick mortality, and eventually raised fewer young to independence (mean adjusted for season: 0.7 +/- 0.16 SE juveniles) than did control pairs (1.2 +/- 0.13). Chick survival was primarily associated with prey availability, and predation risks were not higher in larger broods. 5. Our results provide evidence that incubating unusually large clutches can affect post-hatching performance and lead to lower annual reproductive success in shorebirds. This study, therefore, supports the ILH and points to the importance of monitoring reproductive success beyond the hatching of the chicks.

Reproductive ecology of the invader species gekkonid lizard Hemidactylus mabouia in an area of southeastern Brazil

Hemidactylus mabouia Moreau de Jonnés, 1818 is a "fixed" clutch size exotic species well established in Brazil. In this paper we investigate some reproductive strategies adopted to minimize the costs of invariant clutch size to this invader species living in an environment with marked climatic seasonality in Southeastern Brazil (22°56’S; 46°55’W). The study was carried out from April 2002 to March 2003. Females and males attain maturity at 47.9mm and 46.9mm SVL, respectively. Larger females tended to produce larger eggs. The reproduction occurred throughout the year, but only at the wet season the females increase the clutch frequency. There was a significant variation in mean testis volume among the months throughout the year and the largest means were recorded between August and December. Maternal investment on egg size, increase on clutch frequency and seasonal increase on testis volume can represent important reproductive strategies of this invader species living in an non-urban habitat whit climatic seasonality (dry and cold weather season).

Why reduce clutch size to one or two eggs? Reproductive allometries reveal different evolutionary causes of invariant clutch size in lizards

Summary 1Large clutch size is unambiguously an ancestral state in reptiles. However, females of several lizard lineages lay just one or two eggs per clutch, called invariant clutch size. Selective forces leading to a dramatic drop in fecundity during a single reproductive bout are poorly understood. 2We compared interspecific egg and clutch mass allometries in four lizard lineages with contrasting ways of reproduction. Lacertids and sceloporines have ancestral variable clutch size, while anoles and eublepharid geckos independently evolved invariant clutch size. To reconstruct the anoles’ ancestral situation more precisely, we included data from a member of the closely related genus Polychrus, which is also arboreal but possesses variable clutch size. 3We found the relative mass of the eublepharid double-egg clutch is comparable with the relative mass of the whole clutch in lizards with variable clutch size. Clutch mass in eublepharids and lizards with variable clutch size increases proportionally to female size. However, single-egg anole clutches show similar negative allometry as the sole egg of lizards with variable clutch size. 4It appears that invariant clutch size evolved under (and is maintained by) selection on offspring enlargement in geckos, but selection on reducing female reproductive burden in anoles, i.e. the phenomenon of invariant clutch size apparently evolved in these individual groups for different reasons. 5Besides understanding lizard life history, our study illustrates how singular events in life-history evolution can be reconstructed by comparing the ancestral and evolved reproductive allometries.

Body-size effect on egg size in eublepharid geckos (Squamata: Eublepharidae), lizards with invariant clutch size: negative allometry for egg size in ectotherms is not universal

Within a single clutch, smaller species of ectotherms generally lay a smaller number of relatively larger eggs than do larger species. Many hypotheses explaining both the interspecific negative allometry in egg size and egg size–number trade-off postulate the existence of an upper limit to the egg size of larger species. Specifically, in lizards, large eggs of large species could have too long a duration of incubation, or they could be too large to pass through the pelvic opening, which is presumably constrained mechanically in larger species. Alternatively, negative allometry could be a result of limits affecting eggs of smaller species. Under the latter concept, hatchling size in smaller species may be close to the lower limit imposed by ecological interactions or physiological processes, and therefore smaller species have to invest in relatively larger offspring. Contrary to these lower limit hypotheses, explanations based on the existence of an upper limit always predict negative egg-size allometry even in animals with invariant clutch size, in which naturally there is no egg size–number trade-off. We studied egg-size allometry in lizards of the family Eublepharidae, a monophyletic group of primitive geckos with large variance in body size and an invariant number of two eggs per clutch. We found an isometric relationship between egg and female size that does not support the upper limit hypotheses. © 2006 The Linnean Society of London, Biological Journal of the Linnean Society, 2006, 88, 527–532.

The effects of maternal size on clutch traits in a tropical invariant-clutch lizard, Carlia rubrigularis (Scincidae)

AbstractSpecies with an invariant or "fixed" clutch offer a unique opportunity to examine how variation in maternal size relates to key reproductive traits, such as egg size. Theoretical models of offspring size suggest selection should operate to optimize egg size and reproductive output. However, because invariant-clutch species are unable to allocate surplus resources to additional eggs (or offspring) they may exhibit different relationships than those anticipated under theoretical expectations. To test this, I examined relationships between maternal size-egg size in Carlia rubrigularis, an invariant-clutch producing scincid lizard from tropical Australia. C. rubrigularis exhibited relative clutch masses that were lower than variant clutch size species, but which were similar to other invariant clutch size species. However, maternal size (snout-vent length and post-oviposition mass) was correlated with several clutch traits (egg mass, egg width and egg volume), but females in better condition did not produce relatively heavier eggs. These results suggest mechanistic hypotheses may best explain the observed maternal size-egg size relationships in C. rubrigularis.

Seasonal Declines in the Fecundity of Arctic-Breeding Sandpipers: Different Tactics in Two Species with an Invariant Clutch Size

The breeding biology of Western and Semipalmated Sandpipers was studied for four years near Nome, Alaska. Despite a short breeding season and a putatively invariant clutch size, there were seasonal declines in the fecundity of both sandpiper species. Most females produced only one clutch ( > 98%), but often laid fewer than four eggs (7.6-34.5% of first nests). Clutches of 2-3 eggs were initiated significantly later (6-8 d) and contained smaller eggs (2.9-3.5%) than 4-egg clutches. Small clutches were not renesting attempts, and were not caused by disturbance during laying or partial clutch loss. This is one of the first reports of seasonal declines in egg number among birds considered to have an invariant clutch size. We evaluated four explanations for the seasonal declines in fecundity. The data did not support a clutch size-egg size tradeoff or the nutrient-reallocation hypothesis, but it was not possible to evaluate the cost-of-delay hypothesis. Variation in parent quality was the most likely explanation for the seasonal declines in fecundity. Females that were familiar with the study area bred significantly earlier in Western Sandpipers (4.5 d) but not Semipalmated Sandpipers (3.5 d, p = 0.07). Timing of clutch initiation was not related to female age in Western Sandpipers or to familiarity with a mate in either species. The two sandpiper species adjusted different components of fecundity: Western Sandpipers typically laid four eggs, and in three of four years there were significant seasonal reductions in egg size among 4-egg clutches. In contrast, Semipalmated Sandpipers laid significantly fewer eggs than Western Sandpipers, but females laying 4-egg clutches did not produce smaller eggs if they laid late in the breeding season. Semipalmated Sandpipers may reduce clutch size because their smaller eggs are close to a minimum threshold size necessary to produce viable precocial young in the

Trade-offs between Reproductive Traits and the Influence of Food Intake during Pregnancy in the Garter Snake, Thamnophis elegans

Trade-offs between Reproductive Traits and the Influence of Food Intake during Pregnancy in the Garter Snake, Thamnophis elegans

Life-history strategies of Australian lizards: a comparison between the tropics and the temperate zone.

Previous studies have suggested that tropical and temperate-zone lizards may differ fundamentally in life histories. We tested the applicability of this idea to Australian species by comparing temperate-zone species of agamid and scincid lizards with their congeners from the seasonal tropics. Data were derived from dissection of 1,941 specimens and from published information. Clutch size and egg size were positively correlated with mean maternal body size in most lizard species from both climatic zones. Mean body size of the lizards studies did not differ between the tropics and the temperate zone, nor did egg or hatchling size. However, tropical skinks showed considerably (approximately 20%) lower clutch size and relative clutch mass than did temperate-zone skinks. This difference was partly due to the higher incidence of species with low, invariant clutch size in the tropical lizard fauna (as seen in other continents as well), but primarily due to a trend for lineages (especially genera) with relatively high fecundity to be more common in the temperate zone than in the tropics. In contrast to studies on African lizards, our data suggested that modification of clutch size between areas has not occurred within genera: congeneric species from the tropics and temperate zone did not differ in clutch size. Production of more than one clutch per annum by individual females was common in both climatic zones. Tropical lizards may differ from temperate-zone species in showing higher reproductive frequencies, more rapid growth and earlier maturation. However, most of these effects may be due to phenotypic responses to environmental conditions (especially longer annual activity season), rather than to genetically based lifehistory adaptations.

Reproductive Tactics of Sympatric Gekkonid Lizards with a Comment on the Evolutionary and Ecological Consequences of Invariant Clutch Size

Four sympatric species of gekkonid lizards were studied simultaneously in northeastern Brazil for 12 months. Lygodactylus klugei was the smallest species and Phyllopezus pollicaris was the largest with Gymnodactylus geckoides and Hemidactylus mabouia intermediate in size. Lygodactylus is diurnal whereas Hemidactylus and Phyllopezus are primarily nocturnal. Gymnodactylus may be partially nocturnal and partially diurnal but is usually active in dark microhabitats. Females are larger than males in two species and sexes were similar in the other two. In L. klugei, the only diurnal species, male head size increased with SVL more rapidly than in females. This sexual dimorphism is most likely a consequence of sexual selection. Sexually dimorphic characters may differ in visuallyoriented lizards compared to auditory-oriented species. Reproduction is continuous in all four species and egg size among species is correlated with female size. Egg size is not correlated with female size within a species. A summary of data on offspring size of additional gekkonids reveals a tight correlation between female size and offspring size. It is suggested that selection for optimal offspring size may be a partial determinant of female body size in species with invariable clutch size. A comparison with sympatric species studied during the same time period adds to the diversity of reproductive strategies exhibited by lizards occurring at the same place. Nearly every known lizard reproductive strategy is represented by at least one species occurring in the semi-arid caatinga of northeast Brazil.