I came across this article a few days ago and it really grasped my interest. Since this topic is relevant to the main characters of this blog–birds, butterflies and all other kinds of species–and might bring you (and me) some consolations on this “jolly” occasion of Singles’ Day (11/11), I thought WHY NOT! This post also includes wholesome recommendations of apps to accompany your nature explorations! Enjoy!
We are all familiar with how our sex is determined: a sperm from our dad carrying either an X or Y sex chromosome darts for his Juliet, the egg from our mom that contributes an X chromosome. Upon their miraculous encounter and union full of chemistry (acrosome and cortical reactions), the zygote is born, which, after a long journey of implantation, embryogenesis and organogenesis, gives rise to us. You, as parents, might have also been fooled by the hoax of “酸生女，碱生男”, the pseudoscientific theory of how the acidity of a mother’s diet could influence which chromosome is passed on to the child. But did you know that external factors, such as temperatures, can actually be the determinant of an offspring’s sex for some species?
These species include reptiles such as sea turtles, and fish. Studies have shown that in a warmer temperature (around 30 degrees Celsius), the offspring sex ratio is heavily tilted towards one sex, and, in a lower temperature (22-27 degrees Celsius), towards the other. The actual ratio and temperature, however, vary from species to species.
Temperature-dependent sex determination in three reptile species: the American alligator (Alligator mississippiensis), the red-eared slider turtle (Trachemys scripta elegans), and the alligator snapping turtle (Macroclemys temminckii). (After Crain and Guillette 1998.)
Interestingly, a study by Graves et. al. in 2007 showed that bearded dragons, a type of lizard, harness two mechanisms of sex determination that are highly interchangeable. Besides temperature, the sex of their offspring is also determined by genetical factors. Instead of X and Y, lizards use another two sex chromosomes, Z and W. The principle of determination is reversed: homozygous individuals (ZZ) are male, and heterozygous ones (ZW) are female. The W chromosome is exclusively inherited from the mother, whereas in humans, boys get their Y chromosomes from their dads.
A bearded dragon showing off its golden beard 🙂
The same ZW mechanism is adopted by all birds (Avians), as well as butterflies (Lepidoptera).
Bees, however, are famous for another mechanism– haplodiploidy. All males, the worker bees, are haploid, as they were developed from unfertilised eggs, a process dubbed parthenogenesis; all female bees and the queen bee, on the other hand, are diploid and came about in fertilisation. This matriarchy gives rise to a unique evolutionary strategy of kin selection, whereby individuals would support the reproductive success of their siblings even at the expense of their own disadvantages.
I could talk on and on about bees … (My one-year love-and-hate relationship with these honeymakers oh my) Wait for another blog post about these hardworking creatures who do great service to our environment (cough cough)!
Now, let’s recap: animal sex can be determined by environmental or genetic factors. A predominant external factor would be temperature, and genetic factors can be sex or autosomal chromosomes (which are not covered here). Drawing hope from the vibrant scene of sexual fluidity in wildlife, our LGBTQA+ friends are definitely not alone!
But wait, the human Y chromosome is facing a crisis of imminent extinction! To learn more about the reasons behind, check out this article from Quanta magazine: https://www.quantamagazine.org/the-incredible-shrinking-sex-chromosome-20151201/
Now the good stuffs! The naturalist must-have: iNaturalist App! I haven’t tried it on my explorations yet, but am so excited to try it the next time! The guides on species identification are so comprehensive, ranging from birds to insects to mammals. The best part? Guides on biodiversity from around the world are available, so you can create one for your own region, and explore the flora and fauna in a virtual or physical travel across the globe! When you upload an observation, experts worldwide will connect with you to help you pinpoint and learn more about the species. The Singapore version developed by NParks is also user-friendly and more specific to our biodiversity, and is called SGBioAtlas. You can contribute to the Singapore biodiversity database using your observation records!
A demo of species guides on the app iNaturalist.
In love with yoga (learning yoga in India is now on my bucket list),