She seemed to have no control, for five males were piled atop her, just above the lapping surf. However, she is actually mating with only one of those males. He is in better condition, not larger, than the satellite males at this moon-lit, high-tide orgy among the horseshoe crabs on the Florida coast. Perhaps orgy is the wrong word, for it implies a lack of control, and there is little uncontrolled from the perspective of the females. Some mate with a single male, some with several, and the research of H. Jane Brockmann and her students tells us why. Females with a single male are smaller, younger, and lay fewer eggs than the females mating with more than a single male. These differences can be viewed as alternative reproductive strategies, a big topic in animal behavior, and one that was well-represented at the recent meeting of the Animal Behavior Society in Bloomington Indiana 25 – 30 July 2011. I could say more about these improbable looking creatures and wish I could go witness their big day on the beach, and see the red knots eating them, causing their blue blood to ooze. But the time is past this year and there was a lot more to be learned at these wonderful meetings.
The horseshoe crabs do not have parental duties past egg-laying, but a lot of animals do, and in some of them both parents help. This is the case for many birds, including the commonest of all, the house sparrow. Doug Mock and Trish Schwagmeyer have discovered that mom spends more time sitting on the eggs, keeping them warm, than dad does. Why is this no surprise? It could be because those females are not always faithful to their males. This same team and some collaborators found that about a fifth of all babies are reared by a male that is not actually their father, and that this impacts 41% of all males (Whitekiller, Westneat, Schwagmeyer, and Mock, Badge size and extra-pair fertilizations in the house sparrow, The Condor102:342-348, 2000). This may reduce parental care by those cuckolded dads, but Doug was exploring another angle in his talk at this meeting.
What if females are actually better at incubating than males are? I almost hate to say it, for it sounds like such an excuse for the willfully untalented. You cook dinner – you’re so good at it; you make the bed -I can’t get the sheets as tight as you can; he likes it better when you read the bedtime story, and so on (thankfully not part of my own family dynamic). Well, in these little sparrows it turns out mom actually is better at incubating. She has a bigger brood patch – that odd pice of naked skin that she places directly on the eggs to heat them so they can develop properly. In fact, her brood patch is a couple of degrees warmer than her back, while in the male his smaller brood patch is actually cooler than his back. So the developing eggs actually do better with longer periods incubated by mom.
This lovely story tells a lot about the evolutionary approach to behavior. The more you know, the better. There are reasons why females are unfaithful, though they may not be immediately clear since they cheat on males with big status badges as much as they cheat on lesser males. Given that they cheat, males may have evolved to invest a little less in parental care to save time to look for other mating opportunities. This could have caused the evolution of the smaller, cooler, less energetically expensive, brood patch. But mom incubating more given this evolutionary history and the resulting physical conditions could be best for both parents and the developing chicks. Know your organism, as my early mentors, Richard D. Alexander and Jim Lloyd, stressed over and over.
Polistes wasps are one thing I do know, but there is always room for discovery. Along with his advisor, Liz Tibbetts, grad student Michael Sheehan showed that these wasps can recognize each other well if they are from a species where nests are begun by groups of females, Polistes fuscatus. By contrast, the solitary founding Polistes metricus lacks both the variation and the ability to recognize. Mike was able to tease these two things apart with cross-species experiments. Recognition is important to many areas of animal behavior, and can be found in surprising places, as this talk demonstrated. It is no surprise that for it and the associated paper Mike won the meeting’s most prestigious prize, The Allee Award.
I could go on and on, for the excellent talks and posters were many. Our president, Susan Foster, gave an excellent talk on three-spined sticklebacks, using them to explore adaptive radiation and trait plasticity. These fish represent an excellent natural evolutionary experiment, for the marine form invaded different freshwater locations in British Columbia. How they evolved in the freshwater lakes, what changes occurred in parallel, and how lake type could be predictive, forms some of the best evolutionary work tying history, morphology, behavior, and genetics.
The posters were great. I led the judging of the Founders’ award, and so could look only at those posters. I’ll talk more about this later.
What were the general themes? I’ve watched these develop over the decades. Where we once focused on males, and on behaviors generally adaptive for all, we now also look at females, and at individual variability. We use molecular techniques for phylogenies, and for determining parentage. We generate and test hypotheses with experiments or the comparative method. We work on spiders, ants, frogs, dolphins, monkeys, and birds. This is a meeting worth attending, even for the non-specialist. I can’t wait until next year in Albuquerque.
Horseshoe crab mating tactics – H. Jane Brockmann and Sheri L. Johnson
Stan Braude listening intently just before he received a major award for teaching excellence.
President Susan Foster announcing the awards.
IU campus at dawn. The shrine to the drinking fountain.