Sunday, August 17, 2008

If an animal mates with another species of animal, is it still bestiality?: Onychophorans and outbreeding depression.

I promised more obscure invertebrates, so here is an onychophoran. Onychophorans are forest leaf litter dwellers. I have never seen one, but I live in hope. Their common-or-garden name, velvet worms, seems to suggest that holding one would feel like being stroked with a piece of velvet. As a presumptive scientist, I have qualms about using a word like 'cute', but look at those little antennae. I'm only human!

Onychophorans are also wonderful because they are freaks. I have a soft spot for animals who exist in distant, unclassifiable, evolutionary backwaters. Onychophorans appear to be related to both insects and annelid worms, but cannot be classified as either. They exist in a phylum all of their own. To put this in perspective, human beings are in the phylum Chordata, along with (more or less) everything else that has a backbone. The phylum Onychophora contains only onychophorans. 

Germaine Greer reputedly remarked the other day that she was an animal. Perhaps Germaine should consider becoming an invertebrate. In the tradition of female-dominated ant, bee and termite societies, and female praying mantises who devour their mates after sex, some onychophorans live under a rigid matriarchal hierarchy. 

The Australian species Euperipatoides rowelli commonly lives in a social group of up to 15 females, males and young. They hunt as a pack, immobilising their prey with a sticky secretion of mucus. The group observes a strict hierarchy in the order in which they feed. The dominant female feeds first, followed by other females, then the males and young. According to biologists who made this discovery, 'hierarchy within the group is established by aggressive-dominant and passive-subordinate behaviours'. At least there are no passive-aggressive onychophorans. 

Aggressive behaviour consists of kicking, biting, chasing and climbing on other individuals. Passive behaviour involves running away or allowing oneself to be climbed on. Females are commonly larger than males, and this may explain their higher status. Onychophorans of this species have been observed running their antennae over others' backs, perhaps to estimate their size and social status. 

However, while it's a dog-eat-dog world inside the onychophoran pack, they close ranks against outsiders. To quote the aforementioned biologists, 'E. rowelli from different groups, ie. from different logs, are met with intense agression'. Perhaps Germaine is right. It seems all too easy to draw parallels with the human condition. Personally, when I see someone from a different log, I can barely contain myself. But first I run my antennae over their back, just in case. 

Unfortunately for onychophorans, fragmentation of their habitat means it's sometimes difficult to find a mate, so they resort not to inbreeding, but to outbreeding. To explain by way of analogy, onychophorans are not like the hillbilly who marries his cousin, but the hillbilly who marries his goat. Unable to find a mate of the same species, they will breed with a different species of onychophoran. As with many cross-species matings, the resulting offspring often have fertility problems, as well as unusual numbers of legs. 

Tuesday, August 12, 2008

God scribbled a penis on the ocean floor: the discovery of Riftia pachyptila

Invertebrates are animals that have no backbone. (Actually, to be technically correct, they have no dorsal notochord, but I want this blog to be intellectually light weight, so let's say the first definition is okay.)

Some invertebrates have captured the popular imagination. There are childrens' films featuring ants and bees. There are no childrens' films that feature cute, talking digenean flukes. You might dress your kid in a T-shirt with a picture of a butterfly. You would not dress her in a shirt with a picture of a tapeworm. Or, for that matter, a nematode, a nemertean, or a nudibranch.

Pycogonids are related to spiders, but Incy Wincy pycogonid never climbed up the water spout. A vestimentiferan never flew away home to find her children missing and her house on fire.

Maybe this is because having your house on fire is a pretty normal state of affairs for vestimentiferans. These animals live around hydrothermal vents on the ocean floor. At great depths, molten rock released below the earth's surface causes hot water to flow up into the ocean.

Before 1977, no one knew vestimentiferans existed. Scientists who were conducting an oceanographic survey from a navy submarine unexpectedly discovered unfamiliar worm-like creatures living around vents at a depth of 2500 metres.

Vestimentiferans live inside a hard tube. They have no mouth or gut. Instead, they are filled with bacteria. The hydrothermal vents release sulphur, which the bacteria digest to produce energy. (This is highly unusual, as most living things have to obtain energy either from eating someone else or from photosynthesis.) The vestimentiferan can then digest the bacteria.

In the words of our normally serious and world-weary lecturer, they are 'easy to remember for the exam because they're the ones that look like a giant penis'. Giant is the right word. Vestimentiferans grow to be 2.5 metres long.

More deeply unpopular invertebrate friends to come!