Caves are a fascinating subject, and through history they’ve been feared, respected, admired but never ignored. However, it’s biota went a long time unnoticed because naturalists reasoned the conditions were tough to have life in them. But everything changed with the discovery in 1700 of an eyeless salamander in Eslovaquia when scientists begun to question what else could be found there. Bioespeleology was born. Also, with a more deep understanding of caves, it is becoming clear that most of them (specially limestone and other solution caves) are like terrestrial environments, with spatial heterogeneity and stable conditions to sustain life.
Caves thrive in biodiversity. Let’s make a quick recount, or it will take forever. Insects are the most representative of all taxa, and coleoptera the most diverse within them. Mollusks, chilopods, diplopods, and a huge arrray of arachnids are also present. The crustaceans are the more diverse aquatic invertebrates, with a big representation of amphipods and isopods. Now, in the vertebrate side fish comprise the mayority of the diversity. Also we can find other vertebrates like salamanders, bats, reptiles like snakes, and birds like the curious oilbird Steatornis caripensis. Now, you must be thinking that these animals should be different from the cave outsiders, and you are right.
Let’s consider now how an animal living in the caverns would look like:
you could think that in the darkness you don’t need eyes or fancy pigmentation, and you are right. Because of the lack of light in caverns there’s no need for any of these. They should be small because of the physical limitations of most caves, but they would have big appendages with more complex chemo- and mechanosensors to compensate for the lose of sight. All of these characteristics are called troglomorphisms.
On the other side, they’re metabolism should be reduced in order to survive more days without food, and the lipid storage increases to give energy to the animal while he’s not eating. What about their behavior? in the darkness most animals would become opportunistic and work on their own. Aggregation and aggression are out of the way.
Have something in mind: Across different species some will or not have these characteristics.Recent advances have clearly show that we can not talk of an arqueotype of the hypogean (underground) organisms. Take fish for example. A third of all hypogean fish are completely pigmented and have well developed eyes.
For an easy classification of animals living in caves, researchers have developed a useful vocabulary.We got the troglobionts; exclusive from caves, troglophyls, that spend part of their lifes in caves and trogloxenes, which habit the caves in a temporal or accidental manner. Also it is common to refer to the aquatic species as stygobionts.
The key to understanding the adaptations to caves resides in a high phenotipic plasticity. Experiments have been conducted where a hypogean larval fish is subjected to ligth and darkness for 30 days. In the darkness, she will have not eyes. But in the presence of light, she would get some big pair of eyes. This ability for gene expression is the core aspect to an evolutionary answer for the colonization of caves.
So how the hell did these animals ended up living in the caves? Do they have some kind of deal with He-Who-Must-Not-Be-Named? Well, for long time the most accepted hypothesis was an accidental colonization, but now we know animals go to cave in response to selective pressures like for seeking shelter and escaping from predators like the bat fish Noctilio leporinus.
Caves are really complex and i have just touched the tip of the iceberg. My message is that they have an incredible biodiversity, which needs a lot more studies and discoveries, and that we need an integrative approach to study them, just like we do in terrestrial environments.