It should come as no surprise to any reader of The G-CAT that I’m a firm believer against the false dichotomy (and yes, I really do love that phrase) of “nature versus nurture.” Primarily, this is because the phrase gives the impression of some kind of counteracting balance between intrinsic (i.e. usually genetic) and extrinsic (i.e. usually environmental) factors and how they play a role in behaviour, ecology and evolution. While both are undoubtedly critical for adaptation by natural selection, posing this as a black-and-white split removes the possibility of interactive traits.
Despite how important the underlying genes are for the formation of proteins and definition of physiology, they are not omnipotent in that regard. In fact, many other factors can influence how genetic traits relate to phenotypic traits: we’ve discussed a number of these in minor detail previously. An example includes interactions across different genes: these can be due to physiological traits encoded by the cumulative presence and nature of many loci (as in quantitative trait loci and polygenic adaptation). Alternatively, one gene may translate to multiple different physiological characters if it shows pleiotropy.
From an evolutionary standpoint again, epigenetics can similarly influence the ‘bang for a buck’ of particular genes. Being able to translate a single gene into many different forms, and for this to be linked to environmental conditions, allows organisms to adapt to a variety of new circumstances without the need for specific adaptive genes to be available. Following this logic, epigenetic variation might be critically important for species with naturally (or unnaturally) low genetic diversity to adapt into the future and survive in an ever-changing world. Thus, epigenetic information might paint a more optimistic outlook for the future: although genetic variation is, without a doubt, one of the most fundamental aspects of adaptability, even horrendously genetically depleted populations and species might still be able to be saved with the right epigenetic diversity.
This is partly where the concept of a ‘model’ comes into it: it’s much easier to pick a particular species to study as a target, and use the information from it to apply to other scenarios. Most people would be familiar with the concept based on medical research: the ‘lab rat’ (or mouse). The common house mouse (Mus musculus) and the brown rat (Rattus norvegicus) are some of the most widely used models for understanding the impact of particular biochemical compounds on physiology and are often used as the testing phase of medical developments before human trials.
Managing and conserving threatened and endangered species in the wild is a difficult process. There are a large number of possible threats, outcomes, and it’s often not clear which of these (or how many of these) are at play at any one given time. Thankfully, there are also a large number of possible conservation tools that we might be able to use to protect, bolster and restore species at risk.
This can lead to a particular paradigm of conservation management: keeping everything separate and pure is ‘best practice’. The logic is that, as these different groups have evolved slightly differently from one another (although there is often a lot of grey area about ‘differently enough’), mixing these groups together is a bad idea. Particularly, this is relevant when we consider translocations (“it’s never acceptable to move an organism from one ESU into another”) and captive breeding programs (“it’s never acceptable to breed two organisms together from different ESUs”). So, why not? Why does it matter if they’re a little different?
Well, the classic reasoning is based on a concept called ‘outbreeding depression’. We’ve mentioned outbreeding depression before, and it is a key concept kept in mind when developing conservation programs. The simplest explanation for outbreeding depression is that evolution, through the strict process of natural selection, has pushed particularly populations to evolve certain genetic variants for a certain selective pressure. These can vary across populations, and it may mean that populations are locally adapted to a specific set of environmental conditions, with the specific set of genetic variants that best allow them to do this.
However, when you mix in the genetic variants that have evolved in a different population, by introducing a foreign individual and allowing them to breed, you essentially ‘tarnish’ the ‘pure’ gene pool of that population with what could be very bad (maladaptive) genes. The hybrid offspring of ‘native’ and this foreign individual will be less adaptive than their ‘pure native’ counterparts, and the overall adaptiveness of the population will decrease as those new variants spread (depending on the number introduced, and how negative those variants are).
You might be familiar with inbreeding depression, which is based on the loss of genetic diversity from having too similar individuals breeding together to produce very genetically ‘weak’ offspring through inbreeding. Outbreeding depression could be thought of as the opposite extreme; breeding too different individuals introduced too many ‘bad’ alleles into the population, diluting the ‘good’ alleles.
It might sound awfully purist to only preserve the local genetic diversity, and to assume that any new variants could be bad and tarnish the gene pool. And, surprisingly enough, this is an area of great debate within conservation genetics.
So, what’s the balance between the two? Is introducing new genetic variation a bad idea, and going to lead to outbreeding depression; or a good idea, and lead to genetic rescue? Of course, many of the details surrounding the translocation of new genetic material is important: how different are the populations? How different are the environments (i.e. natural selection) between them? How well will the target population take up new individuals and genes?
Overall, however, the more recent and well-supported conclusion is that fears regarding outbreeding depression are often strongly exaggerated. Bad alleles that have been introduced into a population can be rapidlypurged by natural selection, and the likelihood of a strongly maladaptive allele spreading throughout the population is unlikely. Secondly, given the lack of genetic diversity in the target population, most that need the genetic rescue are so badly maladaptive as it is (due to genetic drift and lack of available adaptive alleles) that introducing new variants is unlikely to make the situation much worse.
That said, outbreeding depression is not an entirely trivial concept and there are always limitations in genetic rescue procedures. For example, it would be considered a bad idea to mix two different species together and make hybrids, since the difference between two species, compared to two populations, can be a lot stronger and not necessarily a very ‘natural’ process (whereas populations can mix and disjoin relatively regularly).
The reality of conservation management
Conservation science is, at its core, a crisis discipline. It exists solely as an emergency response to the rapid extinction of species and loss of biodiversity across the globe. The time spent trying to evaluate the risk of outbreeding depression – instead of immediately developing genetic rescue programs – can cause species to tick over to the afterlife before we get a clear answer. Although careful consideration and analysis is a requirement of any good conservation program, preventing action due to almost paranoid fear is not a luxury endangered species can afford.
We’ve discussed standing genetic variation before on The G-CAT, but often in a different light (and phrasing). For example, when we’ve talked about founder effect: that is, when a population is formed from only a few different individuals which causes it to be very genetically depauperate. In populations under strong founder effect, there is very little standing genetic variation for natural selection to act upon. This has long been an enigma for many pest species: how have they managed to proliferate so widely when they often originate from so few individuals and lack genetic diversity?
Meaning: Octorokus from [octorok] in Hylian; infletus from [inflate] in Latin.
Translation: inflating octorok; all varieties use an inflatable air sac derived from the swim bladder to float and scan the horizon.
Octorokus infletus hydros [aquatic morphotype]
Octorokus infletus petram [mountain morphotype]
Octorokus infletus silva [forest morphotype]
Octorokus infletus arctus [snow morphotype]
Octorokus infletus imitor [deceptive morphotype]
Kingdom Animalia; Phylum Mollusca; Class Cephalapoda; Order Octopoda; Family Octopididae; GenusOctorokus; Speciesinfletus
The species is found throughout all major habitat regions of Hyrule, with localised morphotypes found within specific habitats. The only major region where the variable octorok is not found is within the Gerudo Desert, suggesting some remnant dependency of standing water.
Habitat choice depends on the physiology of the morphotype; so long as the environment allows the octorok to blend in, it is highly likely there are many around (i.e. unseen).
Behaviour and ecology
The variable octorok is arguably one of the most diverse species within modern Hyrule, exhibiting a large number of different morphotypic forms and occurring in almost all major habitat zones. Historical data suggests that the water octorok (Octorokus infletus hydros) is the most ancestral morphotype, with ancient literature frequently referring to them as sea-bearing or river-traversing organisms. Estimates from the literature suggests that their adaptation to land-based living is a recent evolutionary step which facilitated rapid morphological radiation of the lineage.
Several physiological characteristics unite the variable morphological forms of the octorok into a single identifiable species. Other than the typical body structure of an octopod (eight legs, largely soft body with an elongated mantle region), the primary diagnostic trait of the octorok is the presence of a large ‘balloon’ with the top of the mantle. This appears to be derived from the swim bladder of the ancestral octorok, which has shifted to the cranial region. The octorok can inflate this balloon using air pumped through the gills, filling it and lifting the octorok into the air. All morphotypes use this to scan the surrounding region to identify prey items, including attacking people if aggravated.
Diets of the octorok vary depending on the morphotype and based on the ecological habitat; adaptations to different ecological niches is facilitated by a diverse and generalist diet.
Although limited information is available on the amount of gene flow and population connectivity between different morphotypes, by sheer numbers alone it would appear the variable octorok is highly abundant. Some records of interactions between morphotypes (such as at the water’s edge within forested areas) implies that the different types are not reproductively isolated and can form hybrids: how this impacts resultant hybrid morphotypes and development is unknown. However, given the propensity of morphotypes to be largely limited to their adaptive habitats, it would seem reasonable to assume that some level of population structure is present across types.
The variable octorok appears remarkably diverse in physiology, although the recent nature of their divergence and the observed interactions between morphological types suggests that they are not reproductively isolated. Whether these are the result of phenotypic plasticity, and environmental pressures are responsible for associated physiological changes to different environments, or genetically coded at early stages of development is unknown due to the cryptic nature of octorok spawning.
All octoroks employ strong behavioural and physiological traits for camouflage and ambush predation. Vegetation is usually placed on the top of the cranium of all morphotypes, with the exact species of plant used dependent on the environment (e.g. forest morphotypes will use grasses or ferns, whilst mountain morphotypes will use rocky boulders). The octorok will then dig beneath the surface until just the vegetation is showing, effectively blending in with the environment and only occasionally choosing to surface by using the balloon. Whether this behaviour is passed down genetically or taught from parents is unclear.
Few management actions are recommended for this highly abundant species. However, further research is needed to better understand the highly variable nature and the process of evolution underpinning their diverse morphology. Whether morphotypes are genetically hardwired by inheritance of determinant genes, or whether alterations in gene expression caused by the environmental context of octoroks (i.e. phenotypic plasticity) provides an intriguing avenue of insight into the evolution of Hylian fauna.
Nevertheless, the transition from the marine environment onto the terrestrial landscape appears to be a significant stepping stone in the radiation of morphological structures within the species. How this has been facilitated by the genetic architecture of the octorok is a mystery.