Sunday, May 09, 2004

The Animal Kingdom Celebrates Mother's Day

Since Mother's Day as we celebrate it is very human-centric, and focuses largely on buying Hallmark cards, I thought I'd create a list of the style of Mother's Day cards other species might need to buy.

1. Happy Parent's Day, to the one I call mom and dad
For simultaneous hermaphrodites that self-fertilize.

Simultaneous hermaphrodites are organisms that contain mature male and female reproductive organs in a single individual at the same time. These organisms are also called monoecious organisms, in contrast to dioecious organisms where the male and female reproductive organs are found in separate individuals. Some simultaneous hermaphrodites can self-fertilize, meaning that a single individual combines their own sperm and eggs to produce fertilized zygotes that develop into individuals. The offspring in this case will likely not be clones of the parent (though it is theoretically possible for them to be clones) due to the genetic recombination that occurs during production of the sperm and eggs and the subsequent random combination of the gametes. A vertebrate example of this style of reproduction is the fish Rivulus marmoratus. The coccid Icerya purchasi is an insect hermaphrodite that usually self-fertilizes, though some reproductively active haploid males occur in their populations.

2. Happy Mother's Day, to the one some of my siblings call dad
For simultaneous hermaphrodites that don't self-fertilize and sequential hermaphrodites who have turned female after first being male.

Most simultaneous hermaphrodites do not self-fertilize, and thus offspring will be a combination of the sperm from one individual and the eggs from another individual. The belted sandfish Serranus subligarius reproduces in this style, and during copulation the two interacting individuals trade sexual roles. Most barnacles are also simultaneous non-self-fertilizing hermaphrodites. Even though barnacles are sessile they engage in direct copulation; each individual has a very long penis it extends to find other barnacles.

An individual sequential hermaphrodite can be either male or female, but never both at the same time. These organisms are either born male or female, and depending on the environmental conditions around them can turn into the opposite sex. Sequential hermaphrodites that are born male are called protandrous.

Clownfish, of Finding Nemo fame, are a good example of a protandrous hermaphrodite: the largest individual fish in a group is female, the next smallest is the reproductive male, and the rest are typically non-reproductive. When the largest female is removed from the population the male becomes female, and a non-breeder becomes male. Thus, in Nemo's case Marlin (Nemo's father) should have turned into Marla once Coral (Nemo's mother) disappeared.

3. Happy Mother's Day, to the man we call mom
For sequential hermaphrodites who have turned male after first being female.

Sequential hermaphrodites that begin life as a female are called protogynous. Some reef fish, such as the cleaner wrasse Labroides dimidiatus, are protogynous hermaphrodites. Cleaner wrasses live in groups of 10-15 fish, with the largest being male and the rest female. When the male is removed from the group the largest female will transform into a male.

4. Happy Mother's Day, to the only one who made me what I am
For parthenogenetic reproducers.

Parthenogenetic reproduction occurs when an egg (oocyte) develops without any genetic contributions from another individual. Parthenogenesis is highly varied:
  • In some species adults females can choose to produce offspring through either parthenogenesis or sexual reproduction, often by either fertilizing or not fertilizing an egg. An example of this is honeybees, which produce female offspring (workers and queens) by fertilizing an egg and males (drones) by not fertilizing eggs.
  • In other species only certain life stages have parthenogenetic females, while later life stages are biparental, such as in holocyclic species of aphids like Aphis fabae.
  • Some species are entirely parthenogenetic and never produce males. The desert grassland whiptail Cnemidophorus uniparens exhibits this trait.
Not all offspring produced by parthenogenesis are clones of the parent. In many species meiosis still occurs to produce an egg, meaning that crossing over (and other genetic effects) can still occur, making the offspring likely to be somewhat genetically different from the parent. In some species, however, eggs are produced through mitosis (mitotic parthenogenesis) and thus the offspring are likely to be clones of the parents.

5. Happy Parent's Day, to the only one who made me what I am
For asexually reproducing animals.

Asexually reproducing animals that do not necessarily produce gametes fall into three general categories:
  • Gemmulation involves producing a small clump of cells (a gemmule) that has a protective coating. The gemmule will divide and grow into a new organism given the right environmental cues. Freshwater sponges often produce gemmules to overwinter or to survive the drying out of their ponds.
  • Budding is an unequal division of an organism through mitotic divisions, wherein a small outgrowth eventually matures into an adult. Hydra, freshwater cnidarians, often reproduce in this style; hydra buds are not produced through any action of gametes.
  • Fragmentation is when a multicellular organism breaks into two or more parts, with each part regenerating the lost portions of itself. Annelids (segmented worms) and echinoderms (e.g. sea stars) can reproduce through fragmentation. Many of these organisms might not buy a Parent's Day card, however, because determining which of the divided individuals is the parent is typically fruitless.
  • Fission is often added to lists of animal asexual reproduction, but fission involves the reproduction of a single cell into two or more copies of itself. Since there are no single celled animals, animals cannot reproduce through fission; budding or fragmentation are more appropriate terms.
While some of these organisms, such as sponges, never produce males or females, many of these species can reproduce both asexually and sexually. For instance, hydras can be either male or female, and both males and females can make asexually produced buds.

My SO and I had a debate about how to classify the card these combination asexual and sexual organisms should buy, since an asexually produced hydra could be produced by either a male or a female, and thus could theoretically have either a father or a mother. However, since neither male nor female gametes were involved in producing the asexually produced offspring, we concluded that the offspring in question would thus buy a Parent's Day card, not a Mother's Day card.

And, finally,

6. Happy Mother's Day, mom
For biparental, sexually reproducing organisms.

In light of all the variations above, this seems downright boring: one mother, one father, and no changing sexes.

Thanks to Semantic Compositions, whose holiday themed posts inspired this one.

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