How do you tell one bat species from another if they look the same? Genes, sure. Vocalizations, definitely. Their squeaking differs from one species to another. Then there are morphological clues – for instance, subtle differences in the structure of their skulls and teeth, and penis bone.
Yes, three new species of vesper bat have been identified in Africa by zoologists comparing their genes, their teeth and skulls, their calls and the tiny little bones in their penises, their bacula.
Let us be clear that the penis of your average fruit bat is incredibly impressive. It can look remarkably similar to the human phallus except in color, though it may be slimmer. The fruit bat phallus can be a couple of centimeters in length, if not more. Your average vesper bat – and there are some 500 species of vesper bat – is not as generously endowed. Vesper bat bacula are no more than 2 millimeters long, which is less than 0.1 inches.
“In Latin, this charming term [baculum] means ‘little stick,’” Bruce Patterson, the MacArthur curator of mammals at Chicago’s Field Museum and senior author of the paper, helpfully tells Haaretz.
The paper published in the Zoological Journal of the Linnean Society on Thursday ensued after almost 10 years of field work – talk about a labor of love. The three newly described species were found in Kenya and Uganda, and they likely live elsewhere too.
Vesper bats exist on all continents except Antarctica, and all pretty much look like. They are small with soft grayish-brown fur, “sort of the sparrows of the bat world,” as the research summary puts it. Go tell them apart.
Yet to do that very thing Patterson and equally intrepid colleagues hit the field in their “Batmobile” and went into some extremely onerous places.
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Never mind classifying bats, first you have to find them – and vesper bats are very small, some weighing about as much as five peanuts. They’re also very shy and nocturnal. And they’re under pressure: their numbers are declining, says team member Paul Webala of Kenya’s Maasai Mara University.
So, how did the researchers manage what they achieved? They spared no nook or cranny or cave their attention; they inched into extremely uninviting crevices. And they netted bats and measured them and took samples and recorded their calls – vesper bats are insectivores that navigate and hunt using echolocation.
The next stage was to sequence the genetic samples from the bats, and thusly they realized they had discovered three new species classified in two new genera of bats. “The genetics told us, in no uncertain terms, that we had four very discrete groups and only two of them were named,” Patterson explains. In other words, two groups were unknown.
And the scientists carried out morphological examinations. They examined the bats’ skulls and teeth and found that the various species in each group indeed do cluster together, Patternson tells Haaretz. And they discovered that the bacula can also be divided into the four batty groups. (The picture accompanying this article is of the four vesper bat bacula groups, not the penis bones of the newly discovered species.)
“Most African bat species are not as well documented as our new ones are, so that echolocation calls and bacula are still missing from many of the species out there. Assembling genetic information for all those species was an important first step in putting this puzzle together,” Patterson told Haaretz.
Possession of a baculum – a stand-alone bone not connected to any other skeletal part – goes back very far in mammalian evolution, though it apparently evolved after placental mammals split from the marsupials (who don’t have one). So the bacula seems to be the basal condition of placental mammals and it “floats daintily at the end of the penis,” Scientific American helpfully observes.
It can be pretty tremendous: a couple of feet in the case of the walrus, i.e., about a sixth the length of its body. Or it can be pitiful – a mere 40th of the body length in the case of the ring-tailed lemur.
Over time, quite a few species lost it, including the wonder that is we. Humans do not have penis bones. Nor do hyenas (which are now thought to be more cat than dog); apes don’t have them; and cetaceans and hoofed mammals have been spared. Why?
In 2016, research suggested that the evolutionary rationale behind the loss of the penis bone begins with speculation of why the other species have one: to be better lovers. Or at least more prolonged ones. Yes, the male evolutionarily wants to extend intercourse so the female doesn’t meander off and mate with other males before his sperm has a chance to impact, and the baculum is helpful with this.
So the presence or absence may boil down to mating strategy. If a species tends to monogamy, then the baculum is gratuitous. Apparently, if not certainly, “under high levels of sexual competition, bigger is better when it comes to the penis bone,” SciAm sums up.
But why would bacula differ so widely as to be noticeable (upon close examination) among species that otherwise look so much alike? As the researchers show, the differences between bats that otherwise look pretty indistinguishable are significant. Perhaps, theoreticians suggest, the evolutionary advantage to baculum diversity is in preventing gratuitous whoopee, aka interspecies intercourse, resulting in wasted gametes or unviable offspring.
Regarding the calls, the scientists found that all the newly identified species – all of which squeak at pitches we can’t even hear – differed from the calls of other bats. They squeak for purposes of echolocation, to orient themselves in space and find prey.
To revert again to the noble fruit bat, Israeli researchers found in separate research that they have elaborate conversations. Mainly, they grouse a lot – chiefly the lady bats scolding the males about food, space and relationships. The males’ extraordinary endowment only seems to go so far.