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Evolution of Body Size and Reproductive Tactics
... Because species that show BP standing also use similar postures during combat (BPcombat), we analysed both types of BP collectively as BP. No other group of lizards varies in adult size to the degree shown in varanids (Pianka, 1995(Pianka, , 2004Pianka & King, 2004), with the smallest species at 15-20 cm total length and 8-20 g (Australian pygmy monitors) to the largest of all lizards, the Komodo dragon (V. komodoensis), which can attain a total length of 3 m and a body mass of 150 kg (Auffenberg 1981). ...
... komodoensis), which can attain a total length of 3 m and a body mass of 150 kg (Auffenberg 1981). The extinct (Pleistocene) Varanus (Megalania) prisca, a close relative of V. komodoensis (Conrad, Rieppel & Grande, 2008), was as large as V. komodoensis and estimated to have been 3.45 m in total length and 118-158 kg (Pianka, 1995(Pianka, , 2004Wroe, 2002;Head, FLS & Rayfield, 2009), and others (see authors in Pianka & King, 2004;also, see Gould & MacFadden, 2004) have discussed the ecological and evolutionary significance of body size variation in varanid lizards; hence, based on their findings and conclusions, any analysis of BPs in this group necessarily requires the incorporation of body size. ...
... In this test, when the difference in the -log-likelihood values of two states was smaller than 2.0, an ancestral state reconstruction was considered to be ambiguous; when the difference was greater than 2.0, the state with the higher -log-likelihood value was rejected and the alternative state was chosen as the best estimate of the character state. Other DNA-based analyses of the phylogeny of varanoid lizards support the Ast (2001) topology of Varanus relationships (Jennings & Pianka, 2004;Fitch, Goodman & Donnellan, 2006). The Ast (2001) tree incorporated 40 ingroup taxa (Varanus species) comprising four major clades, i.e. ...
The bipedal posture (BP) and gait of humans are unique evolutionary hallmarks, but similar stances and forms of locomotion have had enormous influences on a range of phylogenetically diverse tetrapods, particularly dinosaurs and birds, and a range of mammalian lineages, including non-human apes. The complex movements involved in bipedalism appear to have modest evolutionary origins, and it is presumed that a stable and erect posture is a prerequisite for erect strides and other bipedal movements. Facultative bipedalism in several lineages of lizards is achieved by running, but some varanid lizards (genus Varanus) exhibit BPs without running. In these cases, BPs (BPstanding) are not used as a form of locomotion; rather, BPstanding is associated with defensive displays, and such postures also probably permit better inspection of the environment. Yet, in other varanids, BPs have been observed only during combat episodes (BPcombat), where both contestants rise together and embrace in the so-called clinch phase. Numerous other species, however, show neither type of BP. Past researchers have commented that only large-bodied varanids exhibit BP, a behaviour that appears to show phylogenetic trends. We termed this idea the King–Green–Pianka (KGP) bipedal hypothesis. In this article, we address two main questions derived from the KGP hypothesis. First, what is the phylogenetic distribution of BP in Varanus and close relatives (varanoids)? Second, is BP positively correlated with the phylogenetic distribution of large body size (e.g. snout–vent length, SVL)? In addition, we asked a related question: do the lengths of the femur and tail show body size-independent adaptive trends in association with BP? Because varanid species that show BPstanding also use these postures during combat (BPcombat), both types of BP were analysed collectively and simply termed BP. Using comparative phylogenetic analyses, the reconstruction of BP required three steps, involving a single gain and two losses. Specifically, BP was widespread in the monophyletic Varanus, and the single gain occurred at the most recent common ancestor of the African clade. The two losses of BP occurred in different clades (Indo-Asian B clade and Indo-Australian Odatria clade). BPs are absent in the sister group to Varanus (Lanthanotus borneensis) and the other outgroup species (Heloderma spp.). Our phylogenetic reconstruction supports the KGP prediction that BP is restricted to large-bodied taxa. Using the Hansen model of adaptive evolution on a limited, but highly relevant morphological dataset (i.e. SVL; femur length, FL; tail length, TL), we demonstrated that these characters were not equivalent in their contribution to the evolution of BP in Varanus. SVL was significantly correlated with BP when modelled in a phylogenetic context, but the model identified random processes as dominant over adaptive evolution, suggesting that a body size threshold might be involved in the evolution of BP. A Brownian motion (BM) model outperformed the selection model in our analysis of relative TL, suggesting that TL and BP evolved independently. The selection model for relative FL outperformed the BM model, indicating that FL and BP share an adaptive history. Our non-phylogenetic analyses involving regression residuals of FL and TL vs. SVL showed no significant correlation between these characters and BP. We suggest that BP in Varanus provides a convergent or analogue model from which to investigate various forms of bipedalism in tetrapod vertebrates, especially other reptiles, such as theropod dinosaurs. Because BPstanding in varanids is possibly an incipient stage to some form of upright locomotion, its inclusion as a general model in evolutionary analyses of bipedalism of vertebrates will probably provide novel and important insights. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 97, 652–663.
... Because no histological data exist for extinct Varanus taxa (most identifiable fossils are limited to skull remains), the question comes to consider their sizes, assuming that the relationship between body length and bone vascularization observed in extant species existed also in fossil forms. Pianka (2004) proposed a medium size, roughly comparable to that of V. indicus (580 mm SVL max ; 1,240 mm total length). However, the oldest fossil attributed to Varanus, V. rusingensis from the Early Miocene of , was actually larger, with a total length of 2 m at least (Clos, 1995; see also Molnar, 2004). ...
... Moreover, the lack of bone canals cannot be considered a synapomorphy between the species that display this feature because the subgenus Odatria and the prasinus species group (subgenus Euprepiosaurus), both of which have avascular bones, are phyletically far from each other and by no means constitute a monophyletic group (synthesis in Pianka, 2004). In brief, within the genus Varanus, the occurrence of a bone tissue void of vascular canals is unrelated to the phylogenetic affinities that exist between subgenera; it rather represents a case of homoplasy at this level. ...
Bone vascular canals occur irregularly in tetrapods; however, the reason why a species has or lacks bone canals remains poorly understood. Basically, this feature could depend on phylogenetic history, or result from diverse causes, especially cortical accretion rate. The Varanidae, a monophyletic clade that includes species with impressive size differences but similar morphologies , is an excellent model for this question. Cortical vascularization was studied in 20 monitor species, on three bones (femur, fibula, and tibia) that differ in their shaft diameters, and in the absolute growth speed of their diaphyseal cortices. In all species smaller than 398 mm SVL (133–397 mm in sample), bone cortices lack vas-cular canals, whereas all larger species (460–1,170 mm in sample) display canals. The size 398–460 mm SVL is thus a threshold for the appearance of the canals. The distribution of vascular and avascular bone tissues among species does not precisely reflect phylogenetic relationships. When present, vascular canals always occur in the femur and tibia, but are less frequent, sparser, and thinner in the fibula. Vascular density increases linearly with specific size but decreases exponentially during individual growth. In most species, canal orientation varies between individuals and is diverse in a single section. No clear relationship exists between canal orientation and vascular density. These results suggest that: a) the occurrence and density of bone vascular canals are basically dependant on specific size, not phylogenetic relationships; b) vascular density reflects the absolute growth rates of bone cortices; c) the orientation of vascular canals is a variable feature independent of phylogeny or growth rate.
... The largest species of extant saurians, including the Komodo dragon, belong to the family Varanidae, commonly referred to as monitor lizards or goannas in Australia. Monitor lizards represent a suitable model for studies of body size (Pianka, 1995(Pianka, , 2004 and scaling of morphological (Christian and Garland, 1996;Thompson and Withers, 1997;Thompson et al., 2008;Packard and Boardman, 2009), lifehistory (Thompson and Pianka, 2001), physiological or behavioural (Schuett, Reiserer and Earley, 2009) traits with this variable. Monitor lizards not only exhibit a great variation in body size 1 -Department of Zoology, Faculty of Science, Charles University in Prague, Viničná 7, CZ-12844 Prague 2, Czech Republic 2 -Prague ZOO, U Trojského Zámku 3, CZ-171 00 Prague 7, Czech Republic 3 -Animal Clinic -Bílá hora,Čistovická 44/413, CZ-163 00 Prague 6, Czech Republic * Corresponding author; e-mail: frynta@centrum.cz ...
... Monitor lizards not only exhibit a great variation in body size 1 -Department of Zoology, Faculty of Science, Charles University in Prague, Viničná 7, CZ-12844 Prague 2, Czech Republic 2 -Prague ZOO, U Trojského Zámku 3, CZ-171 00 Prague 7, Czech Republic 3 -Animal Clinic -Bílá hora,Čistovická 44/413, CZ-163 00 Prague 6, Czech Republic * Corresponding author; e-mail: frynta@centrum.cz along both phylogenetic (Pianka, 1995(Pianka, , 2004 and ontogenetic axes (Auffenberg, 1981), but also vary between the sexes. Fully grown males of most species are larger than the females (Cox, Butler and John-Alder, 2007, for a review see Frýdlová and Frynta, 2010), e.g., the ratio between maximum male and female snoutvent length is 1.39 in V. salvator (Shine et al., 1998a), 1.34 in V. komodoensis (Lutz and Lutz, 1991), 1.33 in V. varius (Carter, 1999), 1.31 in V. bengalensis (Auffenberg, Arain and Khurshid, 1991) and 1.30 in V. indicus (Wikramanayake and Dryden, 1988). ...
In monitor lizards, males are typically larger than conspecific females, but body shape is usually quite similar in both sexes. This not only represents a puzzle worthy of evolutionary explanation, but also makes field sex determination of monitor lizards difficult. We asked whether subtle differences in body shape follow the same pattern as in other sexually dimorphic lizard taxa and thus can be explained by the same selective forces. We tested the hypotheses that (1) females have a longer abdomen due to fecundity selection and (2) males possess bigger heads due to intrasexual selection. We also hypothesised that (3) male monitors show a wider chests and longer upper fore-limbs to win male-male wrestling matches. We monitored ontogeny in 35 mangrove-dwelling monitors (Varanus indicus). Seventeen body measurements were taken every three months up to the age of 24-34 months. Sex was determined by an ultrasonographic imaging. We employed multiple approaches to remove the effect of size and used both confirmation and exploratory statistics. The results revealed that sexual differences in body shape were small and emerged after maturity. Females have a relatively longer abdomen while males wider chest and longer upper fore-limbs. Thus, the differences in body shape between male and female varanid lizards may be attributed to both fecundity and sexual selection.
... Lizards of the genus Varanus vary greatly in size. For example, V. brevicauda are 20 cm in total length and weigh 8–10 g (Pianka, 2004). At the other end of the spectrum, the komodo dragon (Varanus komodoensis) is the largest of the living lizards weighing up to 70 kg and reaching 3 m, but an extinct member of the varanidae family, Varanus prisca, reached 7 m in length and is estimated to have weighed up to 620 kg, 8–9 times the mass of the Komodo dragon (Rich et al., 1985). ...
... Furthermore , some of the marine platynotans, such as mosasaurs, were giants, reaching 15 m in length (Hainosaurus; Molnar, 2004 ). Although platynotans display a range of body sizes, the group contains many members that are considerably larger than other lineages of lizards and the direct ancestral lineage of monitors is thought to have been relatively large (Pianka, 2004 ). As with platynotans , many testudines reach a large body size. ...
The factors that explain the diverse arrangement of the major arteries of tetrapods are not known. Here, I aim to illuminate some of the underpinnings of these patterns. I review the variation in the sauropsid left, right, and dorsal aortae regarding the origin of the gastrointestinal blood vessels and the relative diameters of left and right aortae where they join together to form the dorsal aorta. I focus on these features because the quality of blood that flows through these aortae can vary depending on the state of cardiac shunting and the size of the vessel can provide insight into the quantity of blood borne by the vessels. I then place the information in a phyletic, historical, and ecological context. The plesiomorphic pattern is for the gastrointestinal vessels to arise as segmental arteries from the dorsal aorta, which is formed from the confluence of left and right aortae with similar diameters. The pattern is well conserved with only two major variations. First, in several clades of reptiles (testudines, crocodilians, lizards of the genera Varanus and Hydrosaurus) a substantial portion of the gastrointestinal arteries arises from the left aorta, leaving the diameter of the left aorta smaller than the right at their confluence. I hypothesize that this vascular arrangement facilitates growth by allowing more alkaline blood to flow to the somatic (body wall) and appendicular circulations, which may promote bone deposition and inhibit resorption, whereas hypercapnic, acidic blood flows to the digestive viscera, which may provide CO(2) as a substrate for the synthesis of gastric acid, bicarbonate, fatty acids, glutamine, purine rings, as well as glucose from lactate. Second, in some snakes and lizards with snake-like body forms, such as Amphisbaenidae, the diameters of left and right aortae are asymmetrical at their confluence with the left aorta exceeding the right, but in members of the amphibian order Gymnophiona the right generally exceeds the left. This condition is associated with asymmetrical development of the lungs.
... Since that time, and with the discovery of living Komodo Dragons (V. komodoensis) on the east Indonesian islands of Flores, Rinca and Komodo [3] considerable attention was paid in trying to understand the evolution of body size in monitor lizards [4][5][6]. Though several processes are proposed to explain the evolution of giantism in varanids, two competing hypotheses dominate the literature: autapomorphic giantism (i.e. Island Rule) and phyletic giantism (i.e. ...
... Cope's Rule) [7]. Both processes were previously invoked for the evolution of V. komodoensis [4,6,7]. ...
The largest living lizard species, Varanus komodoensis Ouwens 1912, is vulnerable to extinction, being restricted to a few isolated islands in eastern Indonesia, between Java and Australia, where it is the dominant terrestrial carnivore. Understanding how large-bodied varanids responded to past environmental change underpins long-term management of V. komodoensis populations.
We reconstruct the palaeobiogeography of Neogene giant varanids and identify a new (unnamed) species from the island of Timor. Our data reject the long-held perception that V. komodoensis became a giant because of insular evolution or as a specialist hunter of pygmy Stegodon. Phyletic giantism, coupled with a westward dispersal from mainland Australia, provides the most parsimonious explanation for the palaeodistribution of V. komodoensis and the newly identified species of giant varanid from Timor. Pliocene giant varanid fossils from Australia are morphologically referable to V. komodoensis suggesting an ultimate origin for V. komodoensis on mainland Australia (>3.8 million years ago). Varanus komodoensis body size has remained stable over the last 900,000 years (ka) on Flores, a time marked by major faunal turnovers, extinction of the island's megafauna, the arrival of early hominids by 880 ka, co-existence with Homo floresiensis, and the arrival of modern humans by 10 ka. Within the last 2000 years their populations have contracted severely.
Giant varanids were once a ubiquitous part of Subcontinental Eurasian and Australasian faunas during the Neogene. Extinction played a pivotal role in the reduction of their ranges and diversity throughout the late Quaternary, leaving only V. komodoensis as an isolated long-term survivor. The events over the last two millennia now threaten its future survival.
... Because no histological data exist for extinct Varanus taxa (most identifiable fossils are limited to skull remains), the question comes to consider their sizes, assuming that the relationship between body length and bone vascularization observed in extant species existed also in fossil forms. Pianka (2004) proposed a medium size, roughly comparable to that of V. indicus (580 mm SVL max ; 1,240 mm total length). However, the oldest fossil attributed to Varanus, V. rusingensis from the Early Miocene of , was actually larger, with a total length of 2 m at least (Clos, 1995; see also Molnar, 2004). ...
... Moreover, the lack of bone canals cannot be considered a synapomorphy between the species that display this feature because the subgenus Odatria and the prasinus species group (subgenus Euprepiosaurus), both of which have avascular bones, are phyletically far from each other and by no means constitute a monophyletic group (synthesis in Pianka, 2004). In brief, within the genus Varanus, the occurrence of a bone tissue void of vascular canals is unrelated to the phylogenetic affinities that exist between subgenera; it rather represents a case of homoplasy at this level. ...
Bone vascular canals occur irregularly in tetrapods; however, the reason why a species has or lacks bone canals remains poorly understood. Basically, this feature could depend on phylogenetic history, or result from diverse causes, especially cortical accretion rate. The Varanidae, a monophyletic clade that includes species with impressive size differences but similar morphologies, is an excellent model for this question. Cortical vascularization was studied in 20 monitor species, on three bones (femur, fibula, and tibia) that differ in their shaft diameters, and in the absolute growth speed of their diaphyseal cortices. In all species smaller than 398 mm SVL (133-397 mm in sample), bone cortices lack vascular canals, whereas all larger species (460-1,170 mm in sample) display canals. The size 398-460 mm SVL is thus a threshold for the appearance of the canals. The distribution of vascular and avascular bone tissues among species does not precisely reflect phylogenetic relationships. When present, vascular canals always occur in the femur and tibia, but are less frequent, sparser, and thinner in the fibula. Vascular density increases linearly with specific size but decreases exponentially during individual growth. In most species, canal orientation varies between individuals and is diverse in a single section. No clear relationship exists between canal orientation and vascular density. These results suggest that: a) the occurrence and density of bone vascular canals are basically dependant on specific size, not phylogenetic relationships; b) vascular density reflects the absolute growth rates of bone cortices; c) the orientation of vascular canals is a variable feature independent of phylogeny or growth rate.
... Phylogenetically, monitoring monitor lizards is not only based on variations in body size [19,20] but also variations between sexes. In general, the body size of adult males is larger than females [21], but usually the body shape of the two sexes is very similar [22]. ...
The high wealth of monitor lizards in Indonesia has not been matched by the availability of accurate population and distribution data. Even though the data is needed by the Indonesian government to measure the balance between trade volume and the sustainability of monitor lizard populations in the wild. The purpose of writing is to obtain various information about data on blue-tailed monitor lizards. It is hoped that the availability of these data through various educational means can help reduce the burden on the government in predicting, recognizing, and mapping the presence of monitor lizards accurately, so that trade traffic and their population can be controlled and remain sustainable. Methodology through literature review. Writing produces detailed and complete data information about the blue-tailed monitor lizard (Varanus doreanus) which includes morphology and character, sex differences in Varanus doreanus, determining body size, habitat and food, predators, reproductive biology, incubation period and temperature in monitor lizard eggs, distribution and the diversity of monitor lizards that live in Indonesia, conservation status, and studies of monitor lizard ethnozoology.
... Lizards and snakes include about 10, 000 extant species (Uetz et al. 2018) and are distributed nearly worldwide. They show a large range of body sizes, from tiny chameleonids (e.g., Brookesia minima, about 3 cm in total length) to giant forms such as the lizard Varanus [Megalania] priscus and the snake Eunectes murinus (7 m total length : Bellairs 1969;Pianka 2004). They are also ecologically diverse, with semiaquatic (marine iguana), aquatic (Pelamis), fossorial (amphisbaenids) and arboreal (green iguana) taxa. ...
... African and mainland Asian monitors are large and include terrestrial and aquatic species. Small size has evolved independently twice: Once in a clade of monitor lizards from the humid tropics of SE Asia east of Wallace's Line and again in Australia, which hosts its own large clade of pygmy monitors in the subgenus Odatria (Pianka 2004b). Because human population densities are much higher in Africa and Asia than in Australia, African, and Asian monitor lizards face greater threats from humans than do those in Australia. ...
Humans have destroyed vast areas of habitats and fragmented many others. We have modified the atmosphere and in doing so have increased the greenhouse effect, which has changed the climate to produce ever increasing maximum temperatures. Increased temperatures particularly threaten some lizard species in highly biodiverse tropical and sub-tropical regions. Many lizards are also threatened by habitat loss and over-harvesting. Although lizards are ectotherms and might therefore be expected to be resilient to global warming, evidence strongly suggests that many species could be threatened by warming. Some, such as fossorial or nocturnal species or those in cold temperate regions, may be little affected by climate warming but many others such as live bearers and thermoconformer species in tropical forests appear to be particularly vulnerable. The 2011 IUCN Red List of Threatened Species lists 12 lizard species as extinct and another 462 species as critically endangered, endangered or vulnerable. Together, these constitute at least 8.4%, probably more, of all described lizard species. The highly biodiverse lizard fauna of Madagascar is especially threatened mostly due to habitat loss from extensive deforestation.
... However, its presence in Odatria should not be regarded as the mere conservation of a plesiomorphic trait because this clade is supposed to be derived from larger Australian species of the subgenus Varanus (int. al. Sprackland, 1991;King and Green, 1999;Pianka, 2004a). ...
Radiographic and histologic examination of long bone epiphyses in 25 species of Varanoidea (including one Heloderma species) reveals a qualitative difference in epiphyseal development between small and large species. In small monitor lizards, most of them belonging to the subgenus Odatria, metaphyseal plates tend to disappear completely, with fusion of primary and secondary epiphyseal ossification centers in adults that reach an individual body length close to the maximum known for their species. Epiphyseal fusion results in a complete and irreversible arrest of growth. This observation falsifies the previously accepted conclusion that the monitor lizards as a whole have a continuous growth. Conversely, in larger species, morphologically complete growth plates remain present in most (but not all) specimens, including very large adults. Although this feature is not firm evidence of a continuous growth, it nevertheless suggests that large species maintain active growth during ontogeny over a longer period than small species.
... Komodo dragons (Varanus komodoensis), representing the largest extant saurian, are about 14 times longer and even 4118 times heavier than the smallest species V. brevicauda . Thus, varanids are the traditional model for studies tracing the evolution of body size itself (Pianka, 1995(Pianka, , 2004, as well as those examining the scaling of morphological, physiological (Clemente, 2006;Clemente, Thompson & Withers, 2009a;Clemente, Withers & Thompson, 2009b), behavioural (Schuett, Reiserer & Earley, 2009) and life-history (Thompson & Pianka, 2001) variables to body size. The suitability of this model for such analysis is further enhanced by the surprising morphological uniformity of varanids contrasting with the long evolutionary history of their divergence (Fuller, Baverstock & King, 1998;Jennings & Pianka, 2004). ...
In a model group of giant reptiles, we explored the allometric relationships between male and female body size and compared the effects of sexual and fecundity selection, as well as some proximate causes, on macroevolutionary patterns of sexual size dimorphism (SSD). Monitor lizards are a morphologically homogeneous group that has been affected by extreme changes in body size during their evolutionary history, resulting in 14-fold differences among the body sizes of recent species. Here, we analysed data concerning the maximum and/or mean male and female snout-vent lengths in 42 species of monitor lizard from literary sources and supplemented these data with measurements made in zoos. There was a wide scale of SSD from nearly monomorphic species belonging mostly to the subgenus Odatria and Prasinus group of the Euprepriosaurus to apparently male-larger taxa. The variable best explaining SSD was the body size itself; the larger the species, the higher the SSD. This pattern agrees with the currently discussed Rensch's rule, claiming that the relationship between male and female body size is hyperallometric, i.e. the allometric exponent of this relationship exceeds unity and thus SSD increases with body size in the case of male-larger taxa. All our estimates of the reduced major axis regression slopes of this relationship ranged from 1.132 to 1.155. These estimates are significantly higher than unity, and thus unequivocally corroborate the validity of Rensch's rule in this reptilian group. In spite of our expectation that the variation in SSD can be alternatively explained by variables reflecting the strength of sexual selection (presence of male combat), fecundity selection (e.g. clutch size and mass) and/or proximate ecological factors (habitat type), none of these variables had consistent effects on SSD, especially when the data were adjusted to phylogenetic dependence and/or body size.
... Monitor lizards of the family Varanidae are well known as the largest extant saurians, attracting considerable attention from researchers (Pianka et al., 2004). Because this group exhibits great variation in body size along both phylogenetic (Pianka, 1995, 2004) and ontogenetic axes (Auffenberg, 1981), it represents an especially suitable model for studies dealing with body size and scaling of morphological (Christian and Garland, 1996; Thompson and Withers, 1997; Packard and Boardman, 2009), life-history (Thompson and Pianka, 2001), physiological (Clemente et al., 2009a, b) or behavioral (Schuett et al., 2009) traits to this variable. ...
Monitor lizards belong to the largest and the most sexually dimorphic lizards in terms of size, making this group an ideal model for studies analyzing ontogenetic causes of sexual dimorphism. Understanding of these ontogenetic factors is essential to the current discussion concerning patterns of sexual dimorphism in animals. We examined the ontogenetic trajectories of body weight and snout-vent length to analyze the emergence of sexual size dimorphism. Experimental animals were 22 males and 13 females of mangrove-dwelling monitors (Varanus indicus) hatched at the Prague Zoo. They were regularly weighed and measured up to the age of 33-40 months, and subsequently sexed by ultrasonographic imaging. The logistic growth equation was used to describe and analyze the observed growth patterns. Our results confirm considerable sexual size dimorphism in the mangrove monitor. The mean asymptotic body weight of males was nearly three times higher than that of females. As the body size of male and female hatchlings is almost equal, and the growth rate parameter (K) of the logistic growth equation as well as the absolute growth rate up to the age of 12 months do not differ between the sexes, size differences between fully grown males and females should be attributed to timing of the postnatal growth. Males continue to grow several months after they reach the age when the growth of females is already reduced. Therefore, the sexual size dimorphism emerges and sharply increases at this period.
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