Bromance: Sperm Heads Cluster to Get Ahead. In the race towards fertilization, speed matters. And you thought it was size? Researchers found that sperm of many mammals, including the deer mouse Peromyscus, come supplied with hooks so they can literally put their heads together (see image) and swim faster (127.4 μm s−1 ± 3.8 s.e.m. versus 109.8 μm s−1 ± 3.7 s.e.m.). In rats (Rattus norvegicus) for example, ‘trains’ of up to hundreds of sperm link up and boogie together. Yet, only one sperm can fertilize the egg. There is also a hidden danger to this altruism: contact could accidentally trigger the “acrosome” reaction prematurely, and take the sperm out of running altogether. So why do sperm indulge in this risky behavior?
• Polygamy Rules: Did you know that 95% of all mammals are promiscuous? Humans (mostly!) fall in the 5% minority. It is scandalous but true that the female mouse P. maniculatus will mate with successive males as quickly as one minute apart. Scientists reasoned that sperm clustering within a species or within individual males could give a selective evolutionary advantage. They tested this by labeling sperm from different sources red or green. As seen in the image, kinship prevails: so, sperm of a feather flock together. This distinction was even seen between sperm from siblings! Boringly, human sperm do not cluster.
• It’s in your jeans genes: Given that social amoebae like Dictyostelium can aggregate, scientists believe that simple genetics underlie this interesting behavior. New research shows that genetic differences in the immune system distinguish promiscuous species of mice from closely related monogamous species. Other social behavior, that make some animals loners while others to live in groups, is now being studied. Read more: http://goo.gl/kt1Tg