Past Work


Kerstin conducting field work.

The primary goal of my graduate, postdoctoral and early faculty research was to make ecological and evolutionary sense of invertebrate strategies of sex and growth, using manipulative and mensurative experiments and phylogenetic analyses.



Oyster field work.
Kerstin’s graduate students in the field.


Nesting Caspian Terns at ESNERR.

Evolutionary Ecology

Sexual strategies of modular animals

While a bewildering diversity of life-history and growth patterns have been described for marine invertebrates, few have been adequately explained in an ecological or evolutionary context. In a conceptual paper (Wasson & Newberry 1997), I attempted to makes sense of these different modes of sex, and compared their prevalence among modular (clonal and colonial) and unitary animals. I have applied these ideas to a colonial kamptozoan family; field and laboratory experiments revealed diverse sexual modes representing different adaptive strategies (Wasson 1997a, 1998). I experimentally examined the effect of various environmental factors on allocation to sex vs. growth and on allocation to male vs. female functions in a marine bryozoan. In particular, I attempted to determine the resource cost of producing males vs. females, by assessing intra-colonial sex ratios under different food regimes. I also tested prediction that allocation to female function will be higher in small mating groups. For me, the delight as well as the challenge of this research is getting from general models to the specific natural history of the organism, and back again.

The dynamics of fusion

While carrying out some of the above experiments, I serendipitously discovered non-self fusion of colonies in various bryozoan species. I have subsequently attempted to quantify the costs vs. benefits (in terms of growth, reproduction, and survival) to bryozoans of fusing, and to determine how these vary depending on whether they fuse with fragments of themselves, close relatives, or unrelated colonies (Craig & Wasson 2000).

Fusion between two different bryozoan colonies
Bryozoan used for sex allocation experiments

Autotomy in crabs

The propensity of porcelain crab species to shed their limbs at the slightest provocation is another recent research interest. We have demonstrated a strong anti-predatory benefit to cheliped autotomy (Wasson, Lyon & Knope 2002). Moreover, we have discovered that autotomy is a condition-dependent phenomenon: small crabs, which are less well able to fend off attacks by fighting, are more likely to autotomize when grabbed by the cheliped than are large crabs (Wasson & Lyon 2005).


A porcelain crab autotomizes, escaping attack by a larger crab.



A kamptozoan species described by Wasson and named for her grandmother, being preyed on by the nudibranch Ancula pacifica Original artwork by Rick Jones
Kerstin with her daughter Fionna.

Short-term ecological experiments are one way of understanding patterns of sex and growth, but mapping life-history traits onto a robust phylogeny provides equally revealing ways of testing hypotheses, by using evolutionary information to shed light on ecological strategies. I therefore have carried out systematic analyses of my model systems. Given the scarcity of invertebrate systematists, I quickly became a world expert on the phylum Kamptozoa. On invitation and funded by the Australian government, I surveyed the virtually unknown kamptozoan fauna of Australia and New Zealand (Wasson 1995; Wasson & Shepherd 1997; Wasson 2002). I studied the systematics of Caribbean kamptozoans, based on fieldwork on sponge-dwelling kamptozoans in Belize . I also investigated the kamptozoan diversity of the Pacific coast of North America , describing two new species and carrying out the first cladistic analysis of the phylum (Wasson 1997b).

Selected publications

Wasson K. 1995. The kamptozoan Pedicellina whiteleggii Johnston & Walker , 1917 and other pedicellinids from Australia and New Zealand . Records of the South Australian Museum 28(2):131-141

Wasson K, and Newberry AT. 1997. Modular Animals: Gonochoric, hermaphroditic, or both at once? Invertebrate Reproduction and Development . 31:159-175

Wasson K. 1997a. Sexual modes in the colonial kamptozoan genus Barentsia Biological Bulletin 193:163-170

Wasson K. 1997b. Systematic revision of colonial kamptozoans (entoprocts) of the northeastern Pacific. Zoological Journal of the Linnean Society 121:1-63

Wasson K. 1998. Sexual reproduction in the colonial kamptozoan Barentsia hildegardae .Invertebrate Biology 117:123-128

Craig SF, and Wasson K. 2000. Self/Non-self recognition and fusion in the bryozoanHippodiplosia insculpta . Proceedings of the 11 th International Bryozoology Association Conference, pp. 189-196

Wasson K, Lyon , BE, and Knope M. 2002. Hair-trigger autotomy in porcelain crabs is a highly effective escape strategy. Behavioral Ecology 13:481-486

Wasson K. 2002. A review of the invertebrate phylum kamptozoa (Entoprocta) and synopsis of kamptozoan diversity in Australia and New Zealand . Transactions of the Royal Society of South Australia 126:1-20

Wasson K. and Lyon B. 2005. Flight or flight: flexible anti-predatory strategies in porcelain crabs. Behavioral Ecology 16:1037-1041