Victoria McMillan (Research Associate in Biology, Department of Biology; Associate Professor of Scientific Writing, Department of Interdisciplinary Writing) Department of Biology, Colgate University Phone: (315) 228-7713 Fax: (315) 228-7045 E-Mail: VMcMillan@mail.colgate.edu Research Interests: Behavioral ecology, particularly mate-guarding and related behavior in dragonflies. [Details] Teaching Interests: Biology of Insects (BIOL 252), Invertebrate Zoology (Biology 254), Writing in the Natural Sciences (BIOL/COMP 453), Introduction to Writing in the Natural Sciences (COMP 130), Conventions of Grammar (COMP 121), Models of Sickness, Healing, and Health (CORE 126) [Details] Student Research   Publications   Colgate Teaching & Research Directory

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Victoria McMillan

Research Interests:

For over 20 years, I have conducted field studies of reproductive behavior in dragonflies and damselflies (insect order Odonata).  The dragonfly life-cycle includes both an aquatic and a terrestrial stage. The eggs, laid in or near water, give rise to fiercely predaceous larvae that spend weeks or months clambering through the bottom sediments of lakes, ponds, and streams. Eventually, through a process of growth and metamorphosis, the larvae crawl out of the water, shed their skins, and become the familiar winged adults. When sexually mature, both sexes return to the water to reproduce.

            In many odonates, males guard their mates after copulation and during oviposition (egg-laying), during which time the eggs are fertilized with sperm stored in a sac inside the female's body. Researchers have identified two main types of mate-guarding behavior. In contact guarding, or tandem oviposition, the male stays physically attached to the female after mating, and the pair moves about and oviposits as a unit. In non-contact guarding, the male detaches from the female after mating and hovers near her as she oviposits, chasing other males attempting to seize her and inseminate her themselves.

            Since mate-guarding facilitates uninterrupted oviposition, it has obvious advantages for the female. From the male's perspective, the phenomenon has an added twist.  In many odonates, the last male to mate with a female fertilizes most of her eggs. In some species, this "last-male phenomenon" occurs because the male, before copulating, removes previously deposited sperm from the female's storage sac. In other species, sperm deposited by a female's most recent mate displace older sperm to deeper recesses of the sac, where they are less likely to be used for fertilization. In any event, the last-male phenomenon makes it advantageous for a male to protect his sperm investment in a female by guarding her after mating and during egg-laying.

            There are potential costs to guarding, however. A given male has only a finite amount of time and energy to allocate to post-copulatory activities, and guarding a particular female may reduce his chances of finding and inseminating others. The behaviors involved in guarding (e.g., rapid flight, interactions with other males, even descent underwater for some species) may also be energetically draining or even hazardous. Theoretically, natural selection may favor males who optimize their mate-guarding behavior-that is, who budget their time and energy between guarding and non-guarding so as to maximize their reproductive success. Guarding "decisions" (how long or how intensely to guard, or whether to guard at all) may vary with such factors as (a) the density of nearby males (and thus the likelihood of female "take-over" by rivals), (b) the availability of other females (and thus the chance of making other matings), and (c) variations in female egg contents (and thus the "value" of particular females to males).

            My initial research focused on guarding variability in Plathemis lydia, a common North American dragonfly with black-spotted wings and a bluish- white abdomen. Males stake out individual territories over the shallow water of ponds, and females flying nearby are quickly seized, inseminated, and guarded during oviposition. I found that male P. lydia do not always show the consistent non-contact guarding described in previous literature. When male densities are high, a guarder hovers close to his female and repels rivals, but if he's the only male at the pond he may make frequent forays away from his mate or abandon her altogether. A guarder also tends to drift farther from his mate as a given oviposition bout progresses; possibly the time elapsed since the beginning of egg-laying functions as an indicator of diminishing female egg contents. Thus, Plathemis males make both subtle and major adjustments in guarding intensity, "fine-tuning" their behavior in response to moment-to-moment changes in their immediate surroundings.       

            My work on Plathemis has led to other research projects.   Some years ago, I began observations on Sympetrum vicinum, a small, red dragonfly locally common at lakes and ponds in the fall.  S. vicinum is the last dragonfly you will see in the Hamilton area before the onset of winter; it survives brief exposures to snow and breeds even into late October.  Unlike P. lydia, S. vicinum males are not territorial and perform contact, rather than non- contact, guarding. Although unmated males perch near ovipositing pairs, ready to capitalize on any mating opportunities that present themselves, partners rarely detach until the last eggs are laid; hence, take-overs of already-paired females are uncommon. Whereas P. lydia males show some variability in their post-copulatory behavior, S. vicinum males seem rather rigidly programmed to contact guard throughout oviposition. Contact guarding is certainly safer, since rival males can't seize a female who is still physically attached to her mate. However, contact guarding prevents the guarder from clasping other females and thus making additional matings.  My research suggests that such persistent contact guarding by S. vicinum males reflects the low probability that individual males will mate more than once per day, perhaps because other receptive females are scarce and difficult to find.

            My next project on S. vicinum was to look more closely at its conspicuous tendency towards communal oviposition. I had noticed that ovipositing pairs tended to congregate at common oviposition sites, sometimes forming large aggregations. Incoming pairs even seemed to zero in on other pairs already present at the pond. At communal oviposition sites, pairs often jostled one another during the process of egg-laying, and occasionally two pairs even collided in mid-air. I wondered about the costs and benefits of aggregating in this species. Potential drawbacks could be lowered oviposition efficiency and even physical damage from clashes with other pairs. Also, since frogs move towards and attack ovipositing dragonflies, aggregations might attract more predators. On the other hand, pairs ovipositing in groups might benefit from the well-known "dilution effect"—i.e., the larger a group, the less likely it is that a particular member (or pair) of that group will be preyed upon. In the end, I found that aggregating in S. vicinum does not apparently reduce oviposition efficiency or the risk of injury. Moreover, in addition to the benefits of the dilution effect, pairs in groups are less likely to be attacked by frogs than are single pairs because aggregations tend to form in frog-free areas.

            A third species that has figured in my research is Libellula pulchella, a beautiful black-and-white spotted dragonfly common in this area throughout most of the summer. As in P. lydia, L. pulchella males display non-contact guarding and (weak) territoriality. My recent paper on this species, in Journal of Insect Behavior, describes oviposition and post-copulatory behavior in this species, this time with emphasis on female strategies. In dragonflies and many other animals, male behaviors have traditionally received greater attention from ethologists, partly because males are more conspicuous and much easier to study. However, over the past few decades, the evolutionary aspects of female behaviors have begun to receive increased attention, with the result, of course, that we are now compiling a much richer (and more complex) picture of the forces that shape the behavioral ecology of a given species. In the case of L. pulchella, already-mated females in the process of ovipositing face repeated interference from unpaired males trying to capture and inseminate them. My research examined strategies used by females to minimize interference with egg-laying, in the context of the rather weak and sporadic guarding behavior shown by their mates.

            Most recently, my work has focused on Arigomphus villosipes, a dragonfly with quite different behavior from those discussed above.  Also, along with Robert Arnold, I have launched a more extensive project on plant-odonate interactions, since many species of dragonflies and damselflies lay their eggs within plant tissues.  Our first study species was Lestes congener, common here in late fall.  We have since begun to look at a variety of other odonates at field sites in both New York and South Carolina.

            In July 1999, I co-hosted (with Janet Rith ‘81) the 1999 International Congress of Odonatology and First Symposium of the Worldwide Dragonfly Association at Colgate University (Link), and I am currently the North American representative for the WDA.

Teaching Interests:

Biology Department offerings include BIOL 252 (Biology of Insects), BIOL 254 (Invertebrate Zoology), and BIOL 453 (cross-listed as COMP 453).  For the Interdisciplinary Writing Department, I teach COMP 121 (Conventions of Grammar) and COMP 130 (Introduction to Scientific Writing).  For the CORE/Scientific Perspectives  program, I offer CORE 126 (Models of Sickness, Healing, and Health).  

Student Research:

Over the years, I have sponsored various summer research projects involving field studies of local dragonflies.  Topics have included aggressive behavior and territoriality in Plathemis Lydia (Matthew Gelder '94); thermoregulatory and perching  behavior in P. lydia (Kathryn Weibrecht ‘98); female behavioral strategies in P. Lydia (Jann Vendetti ’01); and niche partitioning and competition among among three closely related species of libellulid dragonflies (Michael Wolyniak ’98 and Elizabeth Wolyniak ’05). In the future, there will be opportunities for students to help with ongoing research on plant-dragonfly interactions, as part of a larger project I have undertaken with Robert Arnold.

Recent Selected Publications:

Biology

 

McMillan, V.E. and R.M. Arnold.  2004.  Oviposition behavior and substrate utilization by Lestes congener (Odonata: Lestidae).  International Journal of Odonatology 7(1).  In Press. 

 

McMillan, V .E. 2000. Aggregating behavior during oviposition in the dragonfly Sympetrum vicinum (Hagen) (Odonata: Libellulidae). American MidIand Naturalist 144:11-18.

 

McMillan, V .E.  2000. Postcopulatory behavior in Libellula pulchella Drury (Odonata Libellulidae) and female strategies for avoiding male interference with oviposition.  Journal of Insect Behavior 13(4): 573-583.

 

McMillan, V .E. 2000. Mate-guarding in the Odonata. Invited contribution to Dragonflies Of the World, J. Silsby, ed. CSIRO Publishing, Collingwood, Australia.

 

McMillan, V .E. 1996. Notes on tandem oviposition and other aspects of reproductive behaviour in Sympetrum vicinum {Hagen) (Anisoptera: Libellulidae). Odonatologica 24(2): 187-195.

 

McMillan, V. E. 1991. Variable mate-guarding behaviour in the dragonfly Plathemis Iydia (Odonata: Libellulidae). Animal Behaviour 41: 979-987.

 

 

Scientific writing

 

McMillan, V. and D. Huerta. 2002.  Eye on audience: adaptive strategies for teaching writing. Journal of College Science Teaching 32: 241-45.

 

McMillan, V.E. 2001. Writing papers in the biological sciences, 3rd ed. Bedford Books, Boston. 

 

Huerta, D. and V.E. McMillan. Fall 2000 (No.28). Collaborative instruction by writing and library faculty: a two-tiered approach to the teaching of scientific writing. Issues in Science and Technology Librarianship (online journal). www.library.ucsb.edu/ist/OO-fall/article1.html.