Global Assessment of Reptile Distributions
  • Home
  • About
  • People
  • Activities
  • Meetings
  • Publications
  • Data
  • Links
  • Collaborations
  • BloGARD

Exploring drivers of viviparity amongst global reptiles

5/10/2022

0 Comments

 
Picture Top: Cerastes vipera (a live-bearing viperid snake); bottom: Cerastes cerastes (an egg-laying congener). (Photo: Anna Zimin)
In a recent publication in Global Ecology and Biogeography we (Anna and many others) examined the selective forces that potentially drive the evolution of viviparity (live-bearing) in squamates.
Vertebrates are known for their versatility in reproductive strategies and features. Those, in turn, facilitated their successful expansion across various types of environments worldwide. For instance, the evolution of shelled eggs promoted the expansion of tetrapods into terrestrial habitats, and the retention of eggs inside the parent’s body significantly improved embryo survivability in harsh environmental conditions. Live-bearing (henceforth ‘viviparity’) evolved across all major vertebrate groups, except birds, crocodilians and turtles. Whereas it evolved only once in the mammal history, it is thought to evolve over 100 times independently in squamates (lizards and snakes), with about 20% of their species being viviparous. The prevalence of both egg-laying (oviparity) and viviparity in many squamate clades, and the multiple origins of viviparity, make squamates an excellent model to study the selective forces behind the evolution and biogeography of reproductive modes.
In this study, we aimed to examine most of the common selective forces hypothesized to drive the evolution of viviparity, and the relationship of reproductive mode with body size. Specifically, we tested the predictions that viviparity will be associated with (1) cold climates, (2) unpredictable climates, (3) high elevations (a proxy for hypoxic conditions), and (4) large adult body sizes. In order to do that, we collated a dataset for over 9,000 squamate species (about 80% of non-marine living species), making it the largest-scale study on the subject. Furthermore, because the factors mentioned above may be associated both directly and indirectly (i.e., through another factor) with reproductive mode, we used methods, such as path analysis, that enable to detect and account for such complex relationships.
Our main finding was that viviparity was strongly associated with cold climates, in line with earlier studies. In fact, there are relatively more viviparous than oviparous species in colder climates, and some of the coldest regions occupied by squamates do not include oviparous species at all. Notably, although some warm regions harbor many viviparous species (much more than the coldest climates), such regions usually include even more egg-laying species. The roles of climatic variation and of elevation were found to be less important and not straightforward. Even though the proportions of viviparity at high elevations are higher, elevation probably exerts various selective pressures and influences the prevalence of viviparity primarily through its effect on temperature. Our findings highlight the complexity of processes potentially underlying the evolution of viviparity, but they also provide clear support for low temperatures as selecting for viviparity in squamates.

Picture
Top left: Global richness of viviparous squamate species. Top right: latitudinal variation in richness of viviparous squamate species. Bottom left: Proportion of viviparous squamate species in grid cells. Bottom right: latitudinal variation in proportion of viviparous squamate species.
Author: Anna Zimin
0 Comments

What are the intrinsic and extrinsic drivers of lizard clutch-size evolution?

14/6/2020

0 Comments

 
In a recent publication in Global Ecology and Biogeography GARDians explored the global diversity and distribution of lizard clutch sizes.
Picture
We tested the geographic factors that affect clutch sizes in across nearly 4000 lizard species. We found similar patterns to those that have long been known in birds but were never seriously studied in other groups of organisms: lizards lay large clutches at high latitudes and at highly seasonal regions. We postulate that high latitudes with their short, pronounced productivity peals both allow the production of large clutches and promote putting all the eggs in one basket – because the window of opportunity is short in highly seasonal regions. We hypothesize that this may further be a factor preventing taxa with fixed clutch sizes from colonizing high latitudes.

Picture
Median log‐transformed clutch size in 96 km × 96 km grid cells globally. Top: all lizards; bottom: only lizards with variable clutch sizes. Note that the colour scale differs between the maps. To the right of each map is a curve showing a generalized additive model of the mapped variable (in black), the 95% confidence intervals of the mapped variable per 96‐km latitudinal band (shaded dark grey), and the range of values of the mapped variable per 96‐km latitudinal band (shaded light grey).
Authors: Shai Meiri, Uri Roll
0 Comments

Viviparity does not affect the numbers and sizes of reptile offspring

25/1/2020

1 Comment

 
In a recent publication in the Journal of Animal Ecology we show that the fundamental changes to the mode of life that viviparity brings to squamate females, were surprisingly not reflected in either the number of offspring produced at a single reproductive event (birth, clutch), or their size, or the total mass of offspring produced relative to the size of their mother. The distributions of all these traits in viviparous squamates are remarkably similar to those of oviparous ones. Incidentally we have found that the mass of a recently hatched squamate is (on average, despite much variation) similar to the mass of the egg its mother laid.
Picture
Vipera bornmuelleri on Mt. Hermon (photo Uri Roll)
1 Comment

Birds and Mammals are not that special (in offspring sizes)

25/1/2020

0 Comments

 
In a recently published paper in the Biological Journal of the Linnean Society Shai has shown that the spread of ratios of hatchling or neonate masses to adult masses is very similar across the three classes of amniotes (mammals, birds and, of course, reptiles). This suggests that relatively large offspring are the ancestral and dominant mode of amniotes and have not evolved in response to the elaborate parental care of endotherms
Picture
The relative frequencies of the ratio of offspring size to adult size in mammals (grey), squamates (black) and birds (white). The peak at the smallest ratio is almost entirely composed of metatherians, but mammals (mostly bats) also dominate the highest ratio categories. Note that the range of values is narrower in birds than in either squamates or mammals.
Picture
0 Comments

Global lizard trait database

29/8/2018

0 Comments

 
In a recent publication in Global Ecology and Biogeograpy, I present a vast dataset of over 20 body size, ecological, thermal biology, geographic, phylogenetic and life history traits for global lizards.
Over the past 12 years I have been collecting trait data on lizards to complement GARD’s geographic data and allow asking interesting ecological, evolutionary and biogeographic questions – as well as, hopefully, informing conservation decisions. To this end I've now published geographical, morphological, ecological, physiological and life history data for the 6,657 known species of lizards. In the data paper I present descriptive statistics regarding these traits and point to avenues for future research using the dataset.
Picture
Scincus scincus (Photo: Simon Jamison)
I hope these data will facilitate more study into the biology of these most fascinating of creatures, and that the database publication will encourage others to add yet more data and to correct errors I surely have made when assembling them.

Author: Shai Meiri
0 Comments

Island life only works if you’re easy-going – uncovering predictions of the island syndrome for lizard clutch size variation

18/9/2017

1 Comment

 
In a recent publication in the Journal of Biogeography we show that Insular lizards with variable clutch sizes follow the predictions of the island syndrome, while lizards with fixed clutches do not.
Life-histories of insular species are hypothesized to slow down, a phenomenon known as the "island syndrome". Insular individuals are thus expected to lay smaller clutches of larger eggs compared with individuals belonging to closely related mainland species. Most lizards have variable clutch sizes and can lay any number between one egg and a species-specific maximum, which can be well over 50 eggs. Many lizards, such as geckos and anoles, however, lay invariant small clutches of one or two eggs, and may thus be unable to manifest some aspects of the island syndrome. We tested whether insular species with either variable or invariant clutch sizes respond to insularity differently by analyzing egg, clutch, hatchling and female sizes and brood frequencies of 2,511 lizard species.
Picture
Mediodactylus kotschyi (photo Rachel Schwarz)
Picture
Pafilis & Rachel, Kalogria region NW Peloponnes (photo Shai Meiri)
We found that insular species with variable clutch sizes lay smaller clutches of larger eggs, from which larger hatchlings emerge, compared with mainland species, as expected by the island syndrome. Lizards with invariant clutch sizes, however, lay smaller clutches on islands and increase clutch frequency, compared with mainland species, perhaps because of limitations set by the female body cavity and pelvic opening. This may result from lower seasonality of tropical islands, leading to a greater spread of reproductive effort, or as a result from fluctuations in population densities caused by tropical storms. Our results also emphasize the importance of taking differences in life-history traits into account while studying lizard reproductive traits on large phylogenetic scales.
Picture
Kampana islet (photo: Rachel Schwarz)
Author: Rachel Schwarz
1 Comment

    Author

    Mainly maintained by Shai Meiri and Uri Roll

    Archives

    October 2022
    April 2022
    November 2021
    June 2020
    March 2020
    February 2020
    January 2020
    July 2019
    January 2019
    October 2018
    August 2018
    May 2018
    November 2017
    October 2017
    September 2017
    January 2017
    August 2016
    July 2016
    May 2016

    Categories

    All
    Africa
    Amniotes
    Australia
    Big Data
    Big-data
    Body Size
    Body-size
    Climate
    Clutch Size
    Clutch-size
    Competition
    Conservation
    Deserts & Drylands
    Diet
    Diversification
    Diversity Patterns
    Ecogeographic Rules
    Euroasia
    Evolution
    Extinctions
    Functional Diversity
    GARD History
    Geckos
    Hotspots
    In Memoriam
    Islands
    Island Syndrome
    Late Quaternary
    Latitudinal Diversity Gradient
    Lizards
    Longevity
    Metabolism
    New Guinea
    Nocturnality
    Palearctic
    Priritization
    Reproduction
    Speciation
    Tetrapods
    Tropics
    Type Specimens
    Viviparity
    Wikipedia

    RSS Feed

Powered by Create your own unique website with customizable templates.