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Transcript
Unexpected Resilience of TSD species at the Cretaceous-Palaeogene boundary Summary ● Meteor strike event in Cretaceous-Palaeogene boundary (K-Pg) caused increase in global temperature o volcanic eruptions- lots of CO2 o lots of minerals evaporated-more solar radiation ● GSD vs TSD- how is survival affected o GSD-independent evolving chromosomes could have adaptive benefit o TSD-if extreme temperature changes would extinction result? ● Hypothesized that GSD had more survival than TSD, but actually the opposite! o could be because short term temperature change shifted to more females than more males, or maybe there was actually less climate change than expected, or maybe egg-laying TSD resulted in more protection and less sex skewing than we think... Connections to other readings ● Skinks are also TSD cooler = males warmer = females ● article hypothesized warming from meteors/ volcanoes to cause extinction imbalanced sex ratios cause extinction, but in short term w/ more females, could be beneficial Did your reading clarify any points/ideas? In the instance of the k-pg, TSD seems to have been the advantageous trait over GSD. Whether it is male or female favored sex ratio variance is not known, but most likely femalefavored sex variation is better. Other interesting aspects ● TSD vs. GSD are more resilient in the short-term ● There isn’t a great way to recreate the climate change at the K-Pg boundary ● This is a new area of research! Lots of cool new ideas! Summary ● Previously thought that TSD species would be negatively affected by climate change o Explanation for the extinction of dinosaurs? ● KT boundary: massive climate change due to volcanic eruptions and/or meteor ● 14/16 TSD species survived the KT boundary, while 61% GSD species went extinct ● Think that TSD allowed species to either maintain their sex ratio or shift towards more females (more beneficial for population) ● Maybe the skinks will adapt easily to climate change ● ESD vs GSD ● Global Warming may have begun from CO2 release in India! ● Article clarifies how TSD could be adaptive ● TSD is an example of phenotypic plasticity Y degeneration A single chromosome mutated so all inheritance were male. Y chromosomes can’t line up with X to recombine so they have been evolving separately for millions of years Connects to reading transition of environmental sex determination to genetic sex determination. Losing genes but also gaining genes so is it really disappearing? Decay seems to have come to a halt. Connects to reading transition of environmental sex determination to genetic Y-Chromosome Article ● ● ● ● ● Theory that the Y chromosome might disappear altogether from the genome as it keeps losing genes and does not have a backup copy like other chromosomes Arguments against this theory: o Hasn’t lost any genes within the past 44 million years o Remaining genes may be too essential to lose More responsibilities than simply determining maleness- New genes play a role in sperm production o There has been addition of genes to the Y chromosome o Loss of the Y chromosome in some tissues has already shown to be detrimental Men who lose Y chromosome in bone marrow are at higher risks for cancer and have been shown to die younger Graves in support of her theory: o The Y chromosome has already disappeared in some mammals o Just because the chromosome has gone so long without losing genes doesn’t mean it couldn’t lose them tomorrow Other interesting facts: o The Y chromosome regulates genes differently than the X chromosome which can lead to important consequences in disease prevalence between males and females o 61 of the human Y chromosome’s 78 genes were not present before the first inversion Connection with other material: o This article relates to the figure from the article on sex determination that shows how during the evolution of different species there has been a consistent loss of swappable genes between the X and Y chromosomes with less recombination being seen in the Y chromosome. Avian sex determination • Sex chromosomes: males: ZZ; females: ZW. – Called female heterogamety • In mammals (female XX; male XY) sex determination carried on Y chromosome, expressed in the embryonic male gonad to trigger testis formation. Testosterone relased from the male gonad masculinizes the tissues. • Mechanism for avian sex determination unknown • Might be determined by – Dosage of a Z-linked gene (males have 2, so a larger dosage) – Dominant ovary-determining gene carried on the X sex chromosome – Or both Other things • Fun fact: in chickens, the Z chromosome has has over 350 genes, and the W chromosome has probably less than 20. • This article supplemented on the article we read for Tuesday, Nov. 18th – Sex determination • Mechanisms – Female heterogamety ● ● ● ● birds have genetically determined sex males (ZZ) females (ZW) ZZ→ male or W→ female? ratites are homomorphic (same # genes on sex chromosomes) indicating earlier in evolutionary lineage. (sex chromosomes shortening over evolutionary time) ● triploidy ZZW→shows male and female characteristics ● W chromosome carries female determinant (regardless of number of Z chromosomes)→ implies that W not dominant, can be overridden by ZZ chromosomes so Z dosage and dominant W hypotheses are viable