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  • New study suggests that group nesting should be the norm – not the exception – in reptiles.

    A colony of _Eumeces fasciatus_ brood their eggs.
    A colony of Eumeces fasciatus brood their eggs.

    Continuing my trend of “catching up,” an article in the November issue of Natural History magazine, talks about a new study in the Quarterly Review of Biology, that finds group nesting to be very common place among extant reptiles.

    That study would be:

    Doody, J.S., Freedberg, S., Keogh, J.S.? 2009. Communal Egg-Laying in Reptiles and Amphibians: Evolutionary Patterns and Hypotheses. Quart. Rev. Biol. Vol.84(3):229-252.

    In the paper, Doody et al (no laughing) did a massive search through the herpetological literature (both technical journals, and hobbyist magazines) to look at instances of communal egg laying in reptiles and amphibians (herps). I’m not being hyperbolic here either, as the paper states:

    In total, our assembled database was gathered from 290 different sources, including 176 different scientific journals, 72 books or book chapters, 29 unpublished reports, and 13 unpublished theses. We also have included a number of reliable personal communications from herpetologists.

    What the authors found was that group gatherings of herps are vastly more common than previously believed. Group egg laying was found to be present in 345 reptile species. Now you might be thinking 345 really isn’t all that much for a group composed of some 8700 species.

    Well then aren’t you a Debbie Downer?

    _Ophisaurus attentuatus_ brooding her eggs.
    Ophisaurus attentuatus brooding her eggs.

    Seriously though, the authors address this by mentioning:

    Although the difficulty in locating nests hampers our ability to determine the actual frequency of communal egg-laying among species, we can better estimate this proportion by dividing the number of known communally egg-laying species by the total number of species, excluding those for which eggs have not been found. We conducted such a calculation for the three families of Australian lizards known to include multiple communally egg-laying species—Gekkonidae, Pygopodidae, and Scincidae—as gleaned from the Encyclopedia of Australian Reptiles database (Greer 2004). Proportions of these lizard families known to lay communally were 4–9%, but, when we exclude species for which nests are not known, these values rise dramatically to 73–100%

    The biggest take home message to get from Doody et al’s review, is just how much we don’t know about extant reptiles.

    …the present review highlights our inadequate knowledge of the nests and/or eggs of reptiles. For instance, the eggs or nests are known in only 7% of Australian lizards of the three families that commonly lay communally (N = 411 oviparous spp.) (Greer 2004).The extent of this knowledge for Australian lizards is probably similar to that for reptile eggs on other continents, particularly South America, Africa, and Asia, where the reproductive habits of reptiles are poorly known. This is in stark contrast to other vertebrates such as birds, for which complete field guides to the eggs and nests are available for several continents

    Indeed, just by doing the brief research run needed to compile this blog post, it was apparent that communalism is much more common in reptiles than anyone ever thought. However, because so many of these reports are either anecdotal, or buried in obscure journals, it is easy to miss all the many cases where it is known.

    This discovery lead the authors to the inevitable follow up question of: “why?” What benefit do mothers gain by nesting communally?

    Numerous hypotheses for why animals nest communally, have been proposed.

    • Saturated habitat (only so many suitable nest sites)
    • Sexual selection (choice of males that live in a particular area)
    • Artifact of grouping for other reasons
    • Attack abatement (easier to hide a bunch of eggs in one site, than in multiple sites. Less chance that your eggs will be the ones that are eaten).
    • Maternal Benefits (save time and energy finding a suitable nest site by “freeloading”)
    • Reproductive success (if the nest site worked once before…)
    • Egg insulation

    The authors reviewed all of these possible reasons for communal egg laying in herps. In the end, they found evidence for both the maternal benefits hypothesis, and the reproductive success hypothesis, though they felt a mixed model better explained things.

    Python brooding her eggs.
    Python brooding her eggs.

    Sadly, though the authors mentioned how a lack of information on the natural history of most reptiles is largely responsible for this sudden revelation about their nesting behavior, they nevertheless make repeated mentions of how “social interactions are generally less complex in reptiles and amphibians than in other tetrapods” or how herp sociality forms “relatively simple systems“.

    The reality is that the old view of simplistic “loner” reptiles that only come together to mate, is not accurate. This is especially true for parental care in reptiles.

    The popular view (among the public, and the scientific community) is that reptiles are? “lay’em and leave’em” types when it comes to reproduction. Despite all the herpetological knowledge to the contrary that has been acquired in the past 50 years, it is still popular to spout the party line about reptiles being “uncaring parents.”

    Zoologist Louis Somma took issue with this view of reptilian (in particular, chelonian and lepidosaurian) parenting. He conducted a literature search to see how often mentions of parental care in reptiles are recorded. In the end he wound up finding 1400 references to parental care in reptiles (Somma 2003)!

    Somma’s survey covered various aspects of parental care. He found reported evidence of nest building and / or guarding in tortoises like Manouria emys (McKeown 1999), Gopherus agassizii (Barrett & Humphreys 1986) and 4 other species of chelonian.

    Turning to lepidosaurs, Somma found parental behaviour to be present in 133 species of lizards and 102 species of snakes. Even a species of tuatara (Sphenodon punctatus) is known to guard its nests (Refsnider et al. 2009). Though these numbers appear small compared to the total amount of species that have been described; much like the Doody et al. paper, this is just based off of species whose nesting behaviours we do know. That these taxa all span a wide phylogenetic range, suggests that parental care is more commonplace than initially thought.

    Nest guarding is usually a maternal trait, but some squamates exhibit nest guarding behaviour in both parents, such as some cobra and crotaline snakes (Manthey and Grossman 1997) , as well as tokay geckos (Zaworski 1987).

    Not only active guarding of the nest, but actual brooding of the eggs is also commonly reported in squamates such as various python species (Harlow & Grigg 1984, Lourdais et al. 2007), and skinks (Hasegawa 1985, Somma & Fawcett 1989). Some species are even known to groom their newly hatched young (Somma 1987).

    More interesting still are various reports and observations of parental feeding in some reptile species, such as the skink Eumeces obsoletus (Evans 1959), and the cordylid lizard Cordylus cataphractus (Branch 1998). Not to mention recent evidence of parental feeding in captive crocodylians.

    This leads me to the only reptile group where parental care is well publicized: that of the 23 extant crocodylian species. I could, at this point, list references for parental care in crocodylians. However because this behaviour is so well documented for this group, it would seem unnecessary. It is? better to shed light on the many (MANY) examples of parental care in other reptile species. I also didn’t include related examples like placental evolution in the skink genus Mabuya, or instances of egg binding in captive reptile mothers; due to a lack of appropriate substrate to lay their eggs.

    In the end, the paper by Doody et al. adds to a growing body of evidence which suggests that the “lay’em and leave’em” reptile species of the world, are the exceptions? and not the rule.

    ~ Jura

    Next time: Biomechanics of running suggest “warm-blooded” dinosaurs. Or: why the aerobic capacity model needs to die already.

    References


    Barrett, S.L. & Humphrey, J.A. 1986. Agonistic Interactions Between Gopherus agassizii (Testudinidae)
    and Heloderma suspectum (Helodermatidae). Southwestern Naturalist, 31: 261-263.
    Branch, B.. 1998. Field Guide to Snakes and Other Reptiles of Southern Africa. Third revised edition. Sanibel Island: Ralph Curtis Books Publishing.
    Doody, J.S., Freedberg, S., Keogh, J.S.? 2009. Communal Egg-Laying in Reptiles and Amphibians: Evolutionary Patterns and Hypotheses. Quart. Rev. Biol. Vol.84(3):229-252.
    Evans, L.T. 1959. A Motion Picture Study of Maternal Behavior of the Lizard, Eumeces obsoletus Baird and Girard. Copeia, 1959: 103-110.
    Harlow, P and Grigg, G. 1984. Shivering Thermogenesis in a Brooding Python, Python spilotes spilotes. Copeia. Vol.4:959?965.
    Hasegawa, M. 1985. Effect of Brooding on Egg Mortality in the Lizard Eumeces okadae on Miyake-jima, Izu Islands, Japan. Copeia, 1985: 497-500.
    Lourdais, O., Hoffman, T.C.M., DeNardo, D.F. 2007. Maternal Brooding in the Children’s Python (Antaresia childreni) Promotes Egg Water Balance. J. Comp. Physiol. B. Vol.177:560-577.
    Manthey, U. and W. Grossman. 1997. Amphibein & Reptilien S?dostasiens. Natur und Tier Verlag, M?nster.
    Mckeown, S. 1999. Nest Mounding and Egg Guarding of the Asian Forest Tortoise (Manouria emys). Reptiles, 7(9): 70-83.
    Refsnider, J.M., Keall, S.N., Daugherty, C.H., & Nelson, N.J. 2009. Does nest-guarding in Female Tuatara (Sphenodon punctatus) Reduce Nest Destruction by Conspecific Females? Journal of Herpetology. vol.43(2):294-299.
    Somma, L.A. 1987. Maternal Care of Neonates in the Prairie Skink, Eumeces septentrionalis. Great Basin Naturalist, 47: 536-537.
    Somma, L.A. & Fawcett, J.D. 1989. Brooding Behaviour of the Prairie Skink, Eumeces septentrionalis, and its Relationship to the Hydric Environment of the Nest. Zoological Journal of the Linnean Society. Vol.95: 245-256.
    Somma, L. 2003. parental Behavior in Lepidosaurian and Testudinian Reptiles: A Literature Survey. Krieger Publishing Company. 174pgs. ISBN: 157524201X
    Zaworksi, J.P. 1987. Egg Guarding Behavior by Male Gekko gecko. Bulletin of the Chicago Herpetological Society, 22: 193.
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  • Tuataras do it faster than anyone else.

    Oh yeah, that’s right. You know what I mean.

    This is what we call: subtext

    They evolve…at the molecular level.

    From: Trends in Genetics


    Hay, J., Subramanian, S., Millar, C.D., Mohandesan, E., Lambert, D.M. Rapid molecular evolution in a living fossil. Trends in Genetics
    Vol. 24 (3): 106-109

    Abstract
    The tuatara of New Zealand is a unique reptile that coexisted with dinosaurs and has changed little morphologically from its Cretaceous relatives. Tuatara have very slow metabolic and growth rates, long generation times and slow rates of reproduction. This suggests that the species is likely to exhibit a very slow rate of molecular evolution. Our analysis of ancient and modern tuatara DNA shows that, surprisingly, tuatara have the highest rate of molecular change recorded in vertebrates. Our work also suggests that rates of neutral molecular and phenotypic evolution are decoupled.


    Okay, so what does all that mean? It’s been well established that creatures evolve at rates proportional to their generation times. Animals that have a higher generational turn over, show higher rates of evolution. It’s a simple numbers game. The more offspring one has, the more chances for there to be a beneficial mutation. The shorter the time from birth to reproduction, the faster natural selection can act on these mutations.

    Hence why elephants are not exactly evolutionary racehorses, while insects rule the world. 🙂

    It’s been thought that evolution at the molecular level should mirror what we see on the phenotypic, or morphological level. It makes sense logically. There has to be some connection between molecular evolution and phenotypic evolution. We know that the former gives rise to the latter.

    So if one has a creature that has a short fossil history, or a particularly diverse one, then it suggests it is a fast evolver. Therefore one would expect to see speedy evolution on the molecular level too. This is one of the latest lines of evidence for automatic endothermy (i.e. warm-bloodedness) in dinosaurs and other fossil critters (don’t ask how we have molecular evidence for extinct animals. I just don’t know).

    This latest discovery throws a whole wrench into that mode of thinking. Tuataras (Sphenodon) are one of the slowest animals on the planet. They take a long time to reach sexual maturity (11-13 years). They are commonly referred to as living fossils (though, that really isn’t right). They are the last critter that one would expect to be an evolutionary Speedy Gonzalez.

    Yet, according to the work by Hay et al, that is exactly what has been discovered. Tuataras edge out all other animals studied so far. The closest any other creature comes, is the Ad?lie penguin (Pygoscelis adeliae) of Antarctica. Yet as the graph below shows:

    Tuatara evolution rate

    Tuataras are still significantly faster at their molecular evolution. So then, what does this mean regarding molecular evolution rates vs. morphological ones?

    That’s a good question. The argument of molecular phylogeny vs. morphology, is already a heated one. Morphologists scoff at molecular systematists, while the molecular systematists think morphological phylogeny is pointless since it’s all DNA based anyway. It doesn’t help that molecular data has repeatedly come up with results that fly in the face of morphological based orthodoxy.

    For example:

    Morphologically, tuataras are the sister group to squamates.

    Molecularally, tuataras have been found to nest with crocodiles and birds, in at least one study.

    Molecular systematists have found the false gharial (Tomistoma schlegelli) to nest with the true gharial (Gavialis gangeticus), while morphologists have consistently found T.schlegelli) to be a convergent animal more closely related to true crocodiles. This has resulted in heated back and forth arguments

    Turtles, whose ancestry is still very nebulous, have been found to be anywhere from the base of the diapsid family tree (making them ancestral to all extant reptiles), to offshoots of pareiasaurs, which would place them as offshoots from the main reptile line (basically throwing another 30-50 million years on their divergence from other reptiles).

    Molecular systematics, on the other hand, has found turtles to nest with archosaurs (crocs and birds). A few times (beware: PDF bomb), despite the lack of morphological correlates.

    And then there was just weird stuff during the early days of molecular studies, that didn’t help with its validity problem.

    So both camps are already very skeptical of the other’s findings.

    Now this study suggests that rates of molecular evolution have no relation to morphological rates. Among other things, this seems to make the whole “molecular clock” idea even less tenuous.

    It should be interesting to see what repercussions come from this study.

    ~Jura