When did the first marine reptiles appear?

What is the study of reptile evolution?

Welcome to the study of reptile evolution – Here you’ll be able to trace the lineage of major clades, including the line that ultimately led to humans. You’ll see where and when body parts (= traits) became added, substracted and modified.

What is the history of chromosome analysis in reptiles?

Studies of reptile (nonavian reptiles) chromosomes began well over a century ago (1897) with the initial report on the description of sand lizard (Lacerta agilis) chromosomes. Since then, chromosome analysis in reptiles has contributed significantly to understanding chromosome evolution in vertebrat …

Do thermal and chromosome co-occurrences affect sex determination in reptiles?

Similar co-occurrences of sex chromosomes and thermal effects on sex determination have been observed in other reptiles, fishes, amphibians, and invertebrates (e.g., Dournon et al., 1990, Kozielska et al., 2006, Luckenback et al., 2009 ).

Does nest temperature affect the evolution of sex chromosomes and live-bearing?

Sex determination by nest temperature is proposed to interfere with the evolution of sex chromosomes and live-bearing (ovoviviparity); a negative correlation should thus be observed between TSD and sex chromosomes/live-bearing. Present evidence is consistent with these predictions.

Do highly radiated animal clades have sex-determining chromosomes?

As inferred from the extensive phylogenetic conservatism of sex-determining systems in many highly radiated animal clades (birds, mammals, snakes, iguanids, butterflies and their sister taxon sedge flies), highly differentiated sex chromosomes prevent the switch between male and female heterogamety ( Traut & Marec, 1996; Scherer & Schmid, 2001 ).

How is the sex of squamate reptiles determined?

Squamate reptiles possess two general modes of sex determination: (1) genotypic sex determination (GSD), where the sex of an individual is determined by sex chromosomes, i.e. by sex-specific differences in genotype; and (2) temperature-dependent sex determination (TSD), where sex chromosomes are absent and sex is determined by nongenetic factors.

Is thermal variability important for temperature-dependent sex determination in reptiles?

For reptiles with temperature-dependent sex determination, thermal variability may be as important as thermal averages. Anim. Conserv. 16, 493–494 (2013).

How is the sex of an individual determined in reptiles?

In most animals the sex of an individual is determined at the moment of fertilization; when the egg and the sperm fuse together it is fixed if that animal will be male or female. Yet in many reptilian groups sex determination is established later during incubation, and the determinant external factor is the incubation temperature of the eggs.

Is temperature-dependent sex determination different in birds and reptiles?

Introduction Temperature-dependent sex determination (TSD) during incubation is a well-known phenomenon in reptiles, whereas birds have genotypic sex determination (GSD) in which sex is determined at fertilization long before the incubation of eggs begins (Hardy 2002).

How do incubation temperature and sex chromosomes interact to determine sex?

Reptiles in which both incubation temperature and sex chromosomes interact to determine sex may represent “transitional” evolutionary states between two end points: complete GSD and complete TSD.

Are the mechanisms of sex determination in squamate reptiles phylogenetically labile?

In summary, our analyses have demonstrated that the mechanisms of sex determination in squamate reptiles do not seem to be phylogenetically as labile as usually viewed and that the variability in sex determination is likely to occur only in the gekkotan and agamid + chamaeleonid clades.

What is the ancestral state of squamate reptiles?

TSD emerged as the ancestral state for squamate reptiles after mapping of sex-determining mechanisms onto the morphological phylogeny and the molecular phylogeny according to Townsend et al. (2004). The ancestral state for Lepidosauria (= Rhynchocephalia + Squamata) as well as for Squamata alone is not resolved in the third alternative tree.

What is the adaptive significance of environmental sex determination?

Chromosome-based systems (genotypic sex determination) that generate roughly equal numbers of sons and daughters accord with theory 1, but the adaptive significance of environmental sex determination (that is, when embryonic environmental conditions determine offspring sex, ESD) is a major unsolved problem 2, 3.

How does temperature affect the Sex Ratio in red-eared slider turtles?

Figure 17.20 shows the abrupt temperature-induced change in sex ratios for the red-eared slider turtle. If eggs are incubated below 28°C, all the turtles hatching from them will be male. Above 31°C, every egg gives rise to a female. At temperatures in between, the broods will give rise to individuals of both sexes.

Does incubation temperature affect reproductive success in males and females?

Incubation temperature affected reproductive success differently in males versus females in exactly the way predicted by theory: the fitness of each sex was maximized by the incubation temperature that produces that sex.

What we have learned about sex chromosomes in reptiles?

3.1. What We Learned During the last two decades incredible progress has been accomplished in the knowledge of sex chromosomes in reptiles, and it has profoundly changed our vision about sex determination in reptiles on many points. The first point is the relative abundance of TSD and GSD in reptiles.

Do other sex chromosomes exist in turtles?

2.1.3. General Considerations Are there some possibilities that other sex chromosome systems exist in turtles? Some families such as Trionychidae, Kinosternidae or Emydidae have been highly investigated and offer no hope for this possibility, but some other taxa have been neglected and modern cytogenetics is lacking for them.

Was TSD the ancestral mechanism in squamate reptiles?

TSD is the ancestral state for turtles, and archosaurs possess either TSD (crocodiles) or female heterogamety (birds) ( Janzen & Krenz, 2004 ). Thus, we conclude that regardless of the underlying phylogeny, TSD and the lack of sex chromosomes were probably the ancestral mechanism in squamate reptiles.

Is the evolution of sex-determining mechanisms in squamata restricted to transitions?

We postulate that the evolution of sex-determining mechanisms in Squamata was probably restricted to the transitions from ancestral TSD to GSD. In other words, transitions were from the absence of sex chromosomes to the emergence of sex chromosomes, which have never disappeared and constitute an evolutionary trap.

What can we learn from squamate reptiles?

The rapid accumulation of genomic information from squamate reptiles is generating important new context and insights into the biology, the regulation and diversity of venom toxins, and the evolutionary processes that have generated this diversity.

What do we know about the organelles of squamate reptiles?

of squamate reptiles have been studied most thoroughly to date. This smaller organellar genome functions in mitochondrial genome replication and transcription. Snake mitochondrial genomes

What do we know about the mitochondrial genomes of squamate reptiles?

of squamate reptiles have been studied most thoroughly to date. This smaller organellar genome functions in mitochondrial genome replication and transcription. Snake mitochondrial genomes vertebrates. With the exception of the scolecophidian snakes (blind snakes and their relatives),