Of Mice and Mating “Chooser” Mouse in the Middle, but Delaney Explains That This Set-Up Tended to Stress the Mice Out

RIGHT Now a mental architecture for understanding the capacity for learning depends on their abil- gap between what we understand about the world—in fact, they’re attentive learners. “It ity to grasp abstract relationships: “Infants world and what they understand—there are may be that the reason a baby looks longer have an enormous amount to learn about the nevertheless basic, fundamental relation- when an object seems to go through a wall world, about agents, how they behave, what ships that we may apply to the world in the or when someone chooses a reward that is they want, what they care about. What same way that they do. It may be these rela- less valuable,” Spelke says, “is not that they’re makes that possible? I think it’s possible be- tionships that ultimately are going to help thinking, ‘Something’s wrong here’—but cause they’re able to understand patterns of us understand” why humans are “such in- rather they’re thinking, ‘I must have missed activity in terms of variables like cost and credibly flexible, prolific, creative learners.” something. I didn’t expect that object to go reward.” More ambitiously, infant research vmarina bolotnikova through a wall, so maybe I should pay more may also help bring to light building blocks attention and figure out why that happened.’” of human cognition that cut across human elizabeth spelke website: An immediate implication of the study societies. “Even though infants seem to be harvardlds.org/our-labs/spelke-lab- and others like it, Spelke says, is that infants’ utterly different from us—with this huge spelke-lab-members OUTSIDE THE LOVE BOX mate-choice studies tethered the two “stim- uli”—one mouse from each species—at either end of a Y-shaped chamber, with a third Of Mice and Mating “chooser” mouse in the middle, but Delaney explains that this set-up tended to stress the mice out. She “needed something that hat do Darwin’s finch- not in nature, when they’re running around would allow the mice to physically interact, es and cichlid fish have in in the same plot of woods? but that would still contain the two stim- common? Both animals pro- To find out, she raised some mouse pups uli mice.” So she devised an apparatus she W vide intense parental care, normally—weaned from their parents 23 privately nicknamed “the love box”: three which appears to influence their offspring’s days after birth and separated into same-sex chambers, with the male or female chooser mating preferences later in life. In recent de- cages. Other newborn litters were swapped in the middle and a suitor off in each wing, cades, scientists have proposed this “sexual into nests of nursing females of the oppos- separated by gates pre-programmed to let imprinting” as one of the main mechanisms ing species. When it came time to test all only the chooser move freely. This allowed a that drive explosive speciation within these the newly mature adults’ sexual preferences, wider range of interactions between chooser groups: rapid branching in the tree of life. she tried to make courtship conditions as and candidates: fighting, chasing, nesting, Sexual imprinting has been observed in 15 natural as possible. Generally, past rodent copulation—all of it recorded on video. orders of birds, some fish, and a few mam- mals. Now two species of deer mice (the most abundant mammal in North America) can be added to the list, according to a new paper in Evolution by Emily K. Delaney, Ph.D. ’14, and Hopi Hoekstra, Agassiz professor of zoology: the white-footed mouse (Peromyscus leucopus), and the cotton mouse (Peromyscus gossypinus). Known to produce viable hybrid offspring, these “sister species” have genetic markers suggesting that they diverged rela- tively recently—they’re at what Hoekstra calls the “sweet spot” for scientists inter- ested in speciation. While working in Hoekstra’s lab, Del- aney (now an evolutionary geneticist at the University of California, Davis) planned to study a natural population of hybrids in the field, thinking she might examine the phero- mones involved in mating. But the best-laid schemes of scientists often go awry: out of 316 wild mice that she collected and ran through genetic analysis, only 5 potential- ly fit the profile for hybrids. She therefore switched the focus of her project. The two species mate successfully in the lab—so why Illustration by Marina Micheli Harvard Magazine 15 Reprinted from Harvard Magazine. For more information, contact Harvard Magazine, Inc. at 617-495-5746 RIGHT Now By comparing the preferences of cross-fos- Delaney found evidence for “diet-based...mat- tered with native-raised mice, the research- ers found that same-species preferences are ing”—females in particular seemed to strongly largely determined by sexual imprinting. In other words, cotton and white-footed mice prefer males on the same diet as their parents. choose not to mate with each other in the wild due to learning, rather than genetics. win’s finches, for example, females pair with of their saliva or waste, or just the gener- But the degree of imprinting differs by spe- males that sing songs like their fathers’. In al smells of the nest—impressed on off- cies, and within that, by sex. Cotton mice cichlids from Lake Victoria, females pick ei- spring, who then used that information in preferences can be easily altered by cross- ther red or blue mates based on the moth- adulthood. raising them: in adulthood, they will mate ers who brooded them in their mouths, and Delaney and Hoekstra’s research adds to with a member of their foster species. In scientists think that they’re following either a sharpening portrait of speciation, and the white-footed mice, though, only males seem color or chemical signals. impact of behavior like sexual imprinting. to sexually imprint on their parents, whether Delaney has a hunch about the mechanism But the paper also clears up a question that native or foster; females’ preference for their in deer mice: “I’m almost certain that it’s go- had dogged mammalian ecologists for some own species remains constant regardless of ing to be at least somewhat based on olfac- 75 years: why cotton and white-footed mice who raised them. In the paper, Delaney and tion.” In a follow-up study, she tinkered with won’t mate in nature, but will in captivity. Hoekstra suggest that female white-footed potential imprinting cues by raising some What’s fun, says Hoekstra, is that with new Did you know? mice might imprint on their male siblings litters with parents who drank orange-fla- molecular tools, and an assist from “this (rather than parents), or that any nest-in- vored water, and others with parents who newfangled mate-choice apparatus,” sci- stilled preference for the foster-parent spe- drank garlic-flavored water. Testing their entists can elucidate “this age-old mystery cies might switch after they interact with mate choices (aided again by the “love box”), in the field.” vsophia nguyen the two candidates—especially, say, if the she found evidence for “diet-based assorta- white-footed male seems receptive while the tive mating”—females in particular seemed emily delaney website: cotton mouse male wants to fight. to strongly prefer males on the same diet as emilykdelaney.com What makes offspring imprint? “That’s their parents. Something about what their hopi hoekstra website: the next question,” says Hoekstra. In Dar- parents ate—possibly changing the odors http://hoekstra.oeb.harvard.edu 33% of our funding comes from Sicily, the 10,000 square-mile museum. readers like YOU. Discover the ancient Greek, Roman, Medieval, Renaissance, Baroque and nineteenth-century sites of Sicily on this carefully-paced 13-day tour, brought to you by the leading specialist in cultural vacati ons. We stay in the vibrant citi es of Palermo, Taormina and Syracuse, where we enjoy excepti onal hotels, food and local hospitality. Our tours are accompanied throughout by an archaeologist or art historian, whose expert As a nonproﬁ t afﬁ liate of Harvard University, knowledge brings insight into this diverse island. Harvard Magazine relies on reader donations to ‘So many unexpected treasures – that’s what produce high-quality content and to maintain makes a Marti n Randall vacati on so special.’ editorial independence. 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