Pollinators and Robbers (and Squirrels)

The last tulips in my garden this morning…

It is finally flower season! How I love it! However the happiness of the season is constrained somewhat by the gray squirrels, which have systematically beheaded my tulips (despite the fact that I have been simultaneously trying to ward the pests away with foul chemical sprays and appease them with nuts).  Alas, most of my tulips now lie sad and beheaded beneath the cherry blossoms.

My (ineffective) struggles to protect my beloved tulips remind me of the struggles of wild flowers which face a similar arms race.  The tulips I plant are propagated by big nurseries, and the squirrels don’t really want to eat the blossoms: they merely tear them apart to see if there is any food inside (and (probably) because the miserable rodents enjoy my suffering).   Flowers are plant reproductive organs which exist to repopulate the species.  In the case of garden tulips this involves a complicated relationship between myself, Lowes, tulip farms, nurserymen, and squirrels.  In the world of wildflowers, the players are fewer and the stakes are much higher.

Buff-tailed Sicklebill (Eutoxeres condamini) by Ernst Haeckel

Flowers and their pollinators have a mutualistic relationship:  the hummingbird –or bee, or moth, or bat, or whatever–gets a meal while the flower directly shares its gametes (in the form of pollen stuck to the beak or fur) with distant members of the same plant species.  Some blossoms coevolve to provide nectar to specialized pollinators as with the famous sicklebill hummingbird (which feeds on the nectar of specialized Centropogon and Heliconia flowers which fit the bird’s beak and produce colors appealing to the hummingbirds).

This whole relationship falls apart sometimes though, thanks to a behavior first reported by Charles Darwin. Some animals are nectar robbers.  Lacking the long proboscis or curved beak or special senses necessary to obtain the sweet nectar which the plant offers as a reward for its reproductive interlocutors, some animals simply cut through the blossoms or rip them apart to take the pollen.  Although this can be beneficial (if a robber ends up pollinating a flower anyway, or forces a legitimate pollinating species to travel over a larger area—and thus provide greater genetic diversity), more often it is destructive.

Um, sure I guess…thanks, art department.

Interestingly, a recent study determined that bumble bees learn how to cut holes in flowers and steal the nectar directly from other bumble bees (you can read about the particulars of the study here).  Bumble bees are not the only pollen robbers–various lepidopterans, bats, and birds are guilty in various ways–but the bumble bee example is the first case to prove Darwin’s thesis that such robbing behavior was learned by insects.

It all begins to make more sense now…

Flowers, though passive, are not helpless.  Over generations, they coevolve with both the robbers and the pollinators—which is how they obtain so many convoluted and fanciful forms (and why there are so many toxicologically and pharmacologically active compounds therein).  It is worth thinking about when you encounter a spring landscape of beautiful flowers—beneath the surface lies a world of sex, appetite, and larceny.

The horror!

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Turkeys and Parthenogenesis

Regular readers know how much I esteem turkeys.  Unfortunately I worry that my writings are not winning additional admirers for these astonishing birds.  It is time to play a trump card and reveal one of the great bizarre strengths of turkeys.  They are capable of virgin birth.

A New Mexico Whiptail (Aspidoscelis neomexicana). All New Mexico Whiptails are female. The entire species reproduces by parthenogenesis.

Before you spring up in alarm and start shouting, allow me to present a miniature biology lesson. Parthenogenesis is a form of asexual reproduction. Some female organisms are capable of producing an ovum which develops into a new individual without being fertilized by a male gamete.  In these cases, the mother contributes her genetic material to the offspring.  Although natural parthenogenesis is frequently observed in rotifers, insects, mollusks, crustaceans, and flatworms, this method of reproduction is much less common among vertebrates. However a few species of fish, amphibians, and reptiles are known to reproduce via parthenogenesis (movie-goers may recall that this happened to the dinosaurs in Jurassic Park.)  The turkey is very unusual in being a bird which can reproduce through this means (or at least we think it is unusual—perhaps parthenogenesis is more common among birds then we realize but we just don’t know about it except in settings like farms where it becomes obvious). Chickens can also produce self-fertilized eggs but they almost never develop beyond embryonic stages, whereas female turkeys can and frequently do produce living offspring which lack fathers.

This diagram from the BBC actually explains shark parthenogenesis but you get the idea.

Parthenogenesis occurs in turkeys through the doubling of haploid cells.  Biologists have discovered that the rate at which this occurs can be increased by selective breeding. Poults produced by parthenogenesis are capable of growing into healthy viable toms indistinguishable from toms with more traditional parentage.  You will note that I wrote “toms”—all turkeys conceived via parthenogenesis were created from doubled haploids and are are homogametic. Consequently they are all all male. (This will leave mammal enthusiasts scratching their heads–since female mammals are homogametic and have two x chromosomes. However for birds and for some reptiles, males have two Z chromosomes and thus are the homogametic sex. In such species, females have one Z and one W chromosome and are the heterogametic sex.)

Mammals do not naturally utilize parthenogenesis as a method of reproduction. Certain portions of mammalian genes consist of imprinted regions where portions of genetic data from one parent or the other are inactivated. Mammals born of parthenogenesis must therefore overcome the developmental abnormalities caused by having two sets of maternally imprinted genes.  In normal circumstances this is impossible and embryos created by parthenogenesis are spontaneously rejected from the womb. Biology researchers have now found ways to surmount such obstacles and a fatherless female mouse was successfully created in Tokyo in 2004. With genetic tinkering, human parthenogenesis is also biologically feasible. Before his research was discredited and he was dismissed from his position, the South Korean (mad?) scientist Hwang Woo-Suk unknowingly created human embryos via parthenogenesis. To quote a news article by Chris Williams, “In the course of research, which culminated with false claims that stem cells had been extracted from a cloned human embryo, Hwang’s team succeeded in extracting cells from eggs that had undergone parthenogenesis… The ability to extract embryonic stem cells produced by parthenogenesis means they will be genetically identical to the egg donor. The upshot is a supply of therapeutic cells for women which won’t be rejected by their immune system, without the need for cloning.”

All of which is fascinating to biology researchers (and those who would seek greatly prolonged life via biogenetic technologies), however it seems that in nature, the turkey is the most complicated creature capable of virgin birth.