The weak often revenge themselves on those who use them ill, even though they be the more powerful.
The Eagle and the Beetle, Aesop
Let us consider once again the humble sponge – those (sometimes quite large) plant-like animals of the ocean. Unlike most other creatures, sponges can reproduce both sexually (where an egg and sperm – the gametes formed through meiosis – unite to make a fertilized egg) and asexually (when new creatures come into being in any number of ways that are not sexual reproduction, such as the fission and budding that we saw in the last section).
What is the advantage of one type of reproduction over another? Asexual reproduction tends to be faster (as we saw with bacteria), and copying genes is beneficial if the creature does very well where it lives (its offspring will probably do likewise). Sexual reproduction gives more genetic diversity, helping creatures to thrive in different types of environments.
Bacteria exposed to antibiotics (medicines that help us when we are sick with a bacterial infection) cannot sexually reproduce in order to have a better chance at success. Fortunately for bacteria (and sometimes very unfortunately for us), they do have a way of mixing up their genes with other bacteria: two bacteria who are different from one another will meet up and one of them will give some of their genes to the other (isn’t that nice, they’re sharing). This process, known as bacterial conjugation, increases the amount of diversity in the genes of the creatures in a similar way to having two parents. Sponges also use a combination of sexual and asexual reproduction to survive quite a large variety of environments. They really are remarkable creatures for something that appears to be little more than a bunch of vases or perhaps a large barrel.
Let’s just say, for the sake of argument, that I really hated sponges and wanted to destroy them all (of course, I really like all creatures…well, maybe not fire ants). After all, sponges just sit there like ridiculous ocean-bushes not really doing anything. They even have the audacity to claim to be an animal! So…I think we should destroy them. I’m going to start with this big pink one. How shall I go about it? I know, I’ll cut into tiny pieces. Haha – I have defeated you! Wait, what’s it doing? Each of the pieces is growing into a new sponge. I forgot that sponges can reproduce through regeneration by regrowing from each of many small pieces, like a starfish that can regrow from a single leg or a jade plant can grow from a single leaf. Instead of one dreaded sponge, I now have ten…awesome.
What if I try to freeze it? After all, most sponges live in tropical waters, this should certainly kill it. It’s working – the sponges are breaking up into little balls rolling around on the bottom of the tank. No, wait, this book says that those are reduction bodies which will regrow when the water warms back up…shoot.
Surely they won’t be able to make it if I take them out of the water, right? See, they are breaking apart and getting a bunch of little spots all over them. Hazzah, I will throw you dead sponges back to sea from whence you came! Oh, no, seriously? They’re regrowing again! Those little spots were gemmules (gem-yules) that can regrow even after the sponge has dried out, frozen, or had no oxygen for a while. Bacteria can make themselves into a similarly protective cocoon called a spore, which can survive for centuries (maybe longer) and could make it through the vacuum of space to contaminate other planets. So great, I’ve now got about 50 of these sponges, what can I do?
If I can’t destroy them, I can at least stop them from having babies by putting them in different tanks. Sponges are one of the few animals where each individual can produce both eggs and sperm, but to make a fertilized egg, the gametes have to come from different parents. So, eventually I will defeat them if I separate them…and wait a really long time. Hang on, what is that one doing? I looks like its growing a little sponge on its side – oh no, the sponge is now reproducing through budding (and you thought that was just for unicellular creatures), like a potato growing from a bunch of eyes. Now we have two in this tank…. At least the one in this tank over here is breaking into pieces – I am finally victorious! No, wait, they are all growing into more sponges – this one has reproduced through fission like the bacteria. I give up – the brainless, spineless creature has won. I cannot help but be in awe of such resilient creatures, but I do wish that I still had room for my bed….
P.S. Plants have some other unique ways of reproducing asexually. Take daffodils, for example, they can grow from bulbs – small onion-like structures that form under the ground. Some will grow miniature copies of themselves that can be cut off and planted, such as spider plants and mother of thousands. Many plants that you find in your yard grow through runners that spread just under or even on top of the soil. Apple trees are usually grown from cuttings – branches cut from a tree – because apple seeds will grow into trees with a different kind of apple; oftentimes this is attached or grafted onto another type of tree (often a stronger one) to help it grow. Creatures, even lowly plants, have been created to do amazing things.