Hybrids

    Hybridization seems to be a tricky concept in evolutionary biology. It's an inarguable fact of nature but frameworks like the biological species concept force us to deny it in order to create artificial, human-serving categories. But why is it important? Even though it makes things messy for us, there should be some sort of sense to why it occurs in the first place, right? A beneficial mechanism of communities or perhaps just a happy coincidence of probability and biochemistry?

    While we maybe can't say whether it "exists for a reason" or not, we can definitely see that it has an impact on biological processes. It also presents some challenges in the conservation world (i.e., if you don't know what things constitute a species, how do you protect that species?). In terms of population genetics, hybridization can fix beneficial alleles and it can also dispose of detrimental ones (Quilodrán et al, 2020). So evolutionary, if another "species" has a good line of genetic coding that could benefit another closely related, geographically overlapping species, then when two individuals (or more) decide to make some babies then you instantly have children with a new beneficial allele (or dozens!), assuming they're not reproductively isolated by sterility. If these genes are beneficial enough, then they could quickly spread into the target "species" population via these interbreeding events and reproduction of the alleles by hybrids rearing more and more diluted-hybrid offspring. In simple terms I feel that this could act as a sort of evolutionary springing board: a slew of new genetic material is thrown out into the pool to be acted upon by selection, and if it's good enough, it explodes in the population. A quote from the same paper: "hybrids have the potential to exploit a unique ecology that is intermediate between those of the parental species." While this is in reference to a speciation of yeast, I think that if you extrapolate the information from that quote you can find the gold nuggets of interspecies breeding. Sometimes, it could actually be ecologically beneficial to lose the extremities of two parental species and instead act within an intermediate habitat. If this habitat is novel and made accessible by hybridization, then there's an instead potential for colonization and utilization of that resource the diversifies an ecological community. 

    Interestingly enough, this article also stresses how hybridization can be detrimental to biodiversity. More interesting, it seems to be when it's specifically "forced" anthropogenically, rather than coming about through natural overlap of allopatry. It seems that demographic decline (presumably from habitat loss) and interspecies breeding interact in a negative way to expedite extinction. Radically different allopatric species can bring maladaptive alleles into populations that are on an unwanted genetic extreme, if you will, as opposed to before when geographically related populations could offer genes that were beneficial because of their relatedness. Something known as "speciation reversal" can occur when these maladaptive traits effectively reverse local adaptations and eliminate ecological opportunity.

All in all, it appears that hybridization, like most things, is not good or bad in and of itself. Rather, depending on the context of the hybridization events, biodiversity can either be benefited or damaged according to the background of the interspecies breeding. 

Resources:

Harmonizing hybridization dissonance in conservation; Quilodrán et al. 2020

https://www.nature.com/articles/s42003-020-1116-9

Snail Sex

 Molluscs are fun, in my honest opinion.

Awh, they're hugging!

    They have a range from lil clams to big ass octopuses that are horrifyingly smart. And right in the middle are the wonderful garden snails that leave behind fantastic lil shells for you to collect as a little kid, albeit at the cost of maybe eating your parents' hostas. Quick anatomy rundown on snails: most importantly, they're hermaphrodites, and also, they form special sexy-time swords forged from calcium carbonate and other hard compounds to encourage fertilization of their partners. Love darts, they're called. You may have heard of these in the many popscience platforms that exist. They aren't really "darts" per se, as they aren't fired like projectiles but rather wielded like the lance of a jousting knight.  Why am I talking about this? Well, pipefish seemed fun and cool but I think in terms of sexual evolution and conflict, snails stabbing each other with bone swords is cooler. 

Hm, less cute

    

    I won't go into the physiology of the love dart itself, but I will say that it is developed in the "dart sac" (or bursa teloris) which is part of the snail genital apparatus. It is more or less pushed out from the body like the tongue from the mouth when you're teasing someone, except in this case it falls off. A new love dart must then be formed by the snail. In action, the love dart serves the purpose of secreting hormones that influence the spermoviduct of the opposing snail, which helps to neutralize the recipient's ability to digest sperm cells. This little violent trick can double the fertilization of the recipient snail. Oh, it can also lead to death of the other snail if the other snail has been stabbed by love one too many times.

    My best hypothesis about why this involved has everything to do with the innate truth of sexual conflict: males have to put in less than females. With snails, since they're majority hermaphrodites, then snails in mating essentially compete for who is the acting "male" and "female," thereby competing for who has to devote more energy after the mating ritual. Having a competition of jousting allows for one snail to potentially get the upper hand in insemination and spread more of its genes rather than its opposition/lover. So, perhaps the love dart exists simply to create a gentleman's duel for the sexless snails to decide who must bear the fate of pregnancy and egg-laying. 

    Anyways, you're welcome for sharing everything about snail sex you probably didn't want to know.

Resources:

http://www.molluscs.at/gastropoda/index.html?/gastropoda/morphology/love_dart.html

https://en.wikipedia.org/wiki/Reproductive_system_of_gastropods#:~:text=Gastropods%20are%20capable%20of%20being,the%20opportunity%20to%20self%2Dfertilize.