mike loeb image

Particulars
Postdoctoral Researcher
Section of Evolution and Ecology
University of California at Davis
email: mlloebATucdavisDOTedu
lab phone: 530-752-2937

Research
My work focuses on basic problems in the evolution of social behavior. I am currently trying to understand how cooperation works when groups are large and defectors ("cheats") are hard to police; how parents divvy up care-giving duties without being cheated by the partner; how social systems respond evolutionarily to novel ecological pressures; and other problems in social evolution. I also have an interest in the evolution of life histories and phenotypic plasticity. In my research I use field and lab experiments, molecular genetic markers, and analytical modeling.

Below is a brief sampling of the problems and critters that I work on. The lace bugs (Heteroptera: Tingidae) are especially useful because of their unusual social behaviors but also because many are very easy to culture. I have also begun collaborating with Rick Grosberg on study of a marine snail where males care for offspring that may not be their own. Read on to learn more about these projects.

Gargaphia lace bugs laying eggs
Cooperation and conflict over offspring care.
Caring for offspring is costly. It stands to reason that getting others to pay those costs may be favored by natural selection. But who is going to accept the costs of caring for the offspring of others? Lace bugs may give us an answer. On the left is the eggplant lace bug, Gargaphia solani. These two females are laying eggs together in a communal egg mass on foliage of their host plant, a social behavior first described by Doug Tallamy. In the wild up to four females may oviposit together in a single egg mass. After oviposition, however, all females leave the egg mass except for one lone individual that remains to guard the communal brood against arthropod predators, like this female below that is guarding hatchling nymphs.
Gargaphia lace bug guards nypmphs
This sounds like a costly arrangement for the lone "guard" female, but that's not necessarily the case. One reason is that even though females that abandon their eggs-- "egg dumpers"-- are not burdened with the costs of guarding their first brood, starting their own second clutch in the wild and defending it is not so easy. And as Andy Zink and I have shown, guards may even suppress reproduction of egg dumpers in such a way that favors survival of guard young at the expense of dumper clutch size. Thus, what at first appears to be exploitation of the guard by egg dumpers may not be so after all.

Solenosteira snails with eggs on shell
The marine snail Solenosteira macrospira has similar problems. Here females lay eggs on the shells of males who must then properly care for the eggs without any help. On the left are two males, one without eggs on its shell and the other loaded down with eggs. No one knows if egg carriers are the fathers of those eggs--potentially a huge fitness conflict with females--so Rick and I are using genetic markers called microsatellites to estimate paternity. Stay tuned for more on this weird story.

Group of foraging lace bugs
Cooperation in large groups and the public goods problem.
Cooperation is hard to evolve in interactions between two individuals and even harder in large groups. One reason is because when benefits, or "goods", of cooperation are shared publicly, then it's hard to punish defectors without punishing other cooperators as well. In this next project I am using Gargaphia nymphs to understand how public goods are maintained when defectors are difficult to police. In many lace bugs, nymphs forage on their host plant in dense aggregations (above, right). In the eggplant lace bug nymphal aggregations may contain over 100 individuals, each of which is trying to grow as fast and as large as possible. In the image you can see, in pale green speckled with black, the swath of depleted plant tissues left by a slowly moving lace bug aggregation. The goal of this project is understand how cooperating in foraging groups helps nymphs grow, how this good is distributed within the group, and what potential exists for defection from the costs of foraging.

Pair of Leptobyrsa lace bugs guard nymphs
Social evolution in novel ecological environments.
I also work on populations of a lace bug introduced to the Hawaiian Islands. Leptobyrsa decora is unique among bugs ( "true" bugs, that is) because females not only oviposit communally, but they also remain with the brood and guard together, like this pair on the left. Another special feature of L. decora is that some populations are more inclined towards cooperative care-giving than others, and I'm using Hawaiian populations to determine if there has been an evolutionary response in this trait to novel ecological pressures found on the islands. You can read more about these and other projects at my publications page.