[updated February 3, 2012]

Vikram Kode Iyengar
 
Department of Biology

Villanova University
800 Lancaster Avenue
Villanova, PA  19085
 
email: vikram.iyengar@villanova.edu
office: (610) 519-8081
fax:   (610) 519-7863

 

Research Interests:    
     
Behavioral Ecology, Chemical Ecology, Entomology.  My research involves studying the behavioral ecology of arthropods, with an emphasis on sexual selection in insects. Arthropods are the most abundant and diverse group in the animal kingdom, and they occupy nearly every ecological niche in marine, freshwater and terrestrial habitats. The extraordinary evolutionary success of arthropods can be partly attributed to the remarkable diversity of mating systems, and these fascinating creatures provide many wonderful opportunities to do both field and laboratory studies. My research is driven by my interests in sexual selection and its consequences, and I study many different organisms that communicate through chemistry including moths, beetles and crustaceans. Specifically, I examine how the costs and benefits of mate choice and differences in parental investment shape the evolution of arthropod mating systems. 
     
CURRENT GRADUATE STUDENT(S):  Justin Walsh
   
Utetheisa ornatrix (Lepidoptera: Arctiidae): The Rattlebox Moth
   
Sexual selection is an important area of behavioral ecology that explains phenomena including exaggerated male traits, female mating preferences, precopulatory courtship signals, and postcopulatory sperm selection.  A great deal of my research is focused on the reproductive biology of Utetheisa ornatrix, commonly known as the rattlebox moth.  Tom Eisner introduced me this fascinating lepidopteran during graduate school at Cornell University, and I have been working to unravel its mysteries ever since.
   
The details of this moth's reproductive strategy are complex. Utetheisa, as a larva, feeds on plants of the genus Crotalaria (family Fabaceae), containing poisonous pyrrolizidine alkaloids. Utetheisa is insensitive to the alkaloids, and the larva stores the chemicals systemically, retaining them through metamorphosis into the adult stage. At mating, the male transfers a substantial fraction of his alkaloidal load to the female with the sperm package (spermatophore). The gift is transmitted by the female in part to the eggs, together with a supplement of her own alkaloidal supply. All developmental stages of Utetheisa are protected by the alkaloid, the larvae and adults against spiders, and the eggs are avoided by ants and coccinellid beetles. The spermatophore is of substantial size, amounting on average to over 10% of male body mass. It also contains nutrient, which the female invests in egg production. Females mate on average with four to five males over their lifespan of 3 to 4 weeks. With each mating, the female is able to increase her fecundity by 15%. Fecundity in Utetheisa is also a function of intrinsic female body mass: large females lay greater numbers of eggs.
     
Female Utetheisa do not mate randomly with males but do so selectively with males of higher alkaloid content. The female does not gauge male alkaloid content directly but does so indirectly, on the basis of a pheromone (hydroxydanaidal) that the male produces from alkaloid, in proportion to his alkaloid load, and airs during close-range precopulatory interaction with the female. Males richest in alkaloid, having the strongest pheromonal scent, are also largest, and apt to bestow the largest alkaloidal (and presumably nutritive) gifts. In essence, by selecting males of high alkaloid content, the female is selecting males of large size.
     
My doctoral research established that body size is heritable in Utetheisa. This finding indicated that by favoring larger males, females obtain not only larger nuptial gifts but also larger sons and daughters. The offspring, as a consequence, could receive direct phenotypic benefits (from the nuptial gifts) and indirect genetic benefits (from the expression of largeness in both sons and daughters). Further investigation revealed that the offspring of preferred males do indeed fare better than the offspring of non-preferred males. Specifically, I showed that (i) eggs sired by preferred males are less vulnerable to predation; (ii) sons of preferred males are more successful in courtship; and (iii) daughters of preferred males are more fecund. In Utetheisa, multiple benefits appear to have contributed to the female mating preference for large males, and I am interested in how direct and indirect benefits may interact in the evolution of female choice.
     
As a postdoctoral associate, I continued my research in the areas of behavioral and chemical ecology. My main projects involved testing sexual selection models by quantifying the strength, heritability, and sex-linkage of the female mating preference (for large males) in Utetheisa. In Utetheisa, as in all lepidopterans and birds, males are homogametic (ZZ) whereas females are heterogametic (ZW). Interestingly, the female mating preference gene(s) are Z-linked, which means that they are strictly paternally inherited. In addition to providing support for the protected invasion theory, which links exaggerated male traits with genetic architecture, this result highlights the importance of indirect genetic benefits in the evolution and maintenance of sexual selection in this moth.
     

I am currently working on three projects regarding sexual selection in Utetheisa ornatrix. The first project addresses the relative importance of direct and indirect benefits by using a novel chemical approach to determine the modulation in HD levels based on a male’s mating history. In Utetheisa, females are promiscuous, which is considered unusual because the costs generally outweigh the benefits of multiple mating in females. In this particular insect, however, females can accrue multiple benefits from each mating, as females have been demonstrated to use PAs and nutrients from multiple mates (for defensive purposes and increasing fecundity, respectively) while using the sperm from one male. Recent field studies in Florida found that females on average mated with 11 males over their 3-4 week adult lifespan, which suggests that more paternity studies are required to account for higher levels of female promiscuity. The second project uses microsatellites determine how the siring pattern changes over a female’s lifetime based on the number, quality, and presentation order of multiple mates. Since one male provides enough sperm to fertilize the entire complement of a female’s eggs, any changes in paternity over time are likely to reflect the relative quality of her most recent mate. The third project focuses on larval competition, which is likely to be the heritable trait that drives sexual selection in adults. Utetheisa has been studied for over two decades, and previous research on all aspects of its life history have made it a model system for studying the chemical basis of reproductive behavior. With these projects, I hope further our understanding of fundamental principles of sexual selection as I lay the foundation for future experiments that will advance the expanding, interdisciplinary field of chemical ecology. 

 
     

 

Megalorchestia californiana (Amphipoda: Talitridae): The California Beach Flea
Currently, I am also investigating the mating system and reproductive strategies of the California Beach Flea (Megalorchestia californiana), an amphipod found on sandy beaches from California to Washington. Adults, which reach over 1" in size, are often found roaming the beaches in the evening scavenging washed up animals or eating seaweed. Females spend most of the daytime in burrows that are guarded by males. Competition over females can lead to territorial fights between males looking to control access to the group of females (harem) found inside the burrow. Victorious males get the reward of mating with the females, who brood their eggs in an internal pouch and release fully active juveniles.
     
I was initially interested in M. californiana because there is a sexual dimorphism that is unusual among arthropods in that males are larger than females.  Furthermore, males have larger, redder antennae and an enlarged second pair of gnathopods – both of these characters are used by the male to hold the female and guard her prior to mating. Individuals of both sexes are found in burrows near or beneath beach wrack, and they are scavengers that feed on decaying plant or animal tissue.  Competition for burrows can be fierce, and burrows appear to be a valuable resource by offering protection from predators, prevention of desiccation and a safe place to copulate and breed.   Previous work indicated that these organisms have a harem mating system in which a single male may guard and mate with many females, and our experiences in the field confirmed that multiple females are often found in a burrow with a single male.  Our initial observations revealed that males use their enlarged antennae to prevent other males from removing them from their burrow or to evict smaller males from a burrow.  Although it had been suggested that larger males are more successful in mating with females, we wanted to empirically test aspects of sexual selection including male competition and female choice.  Specifically, we looked at interactions between two males alone and in the presence of a female.
     
We found that both sexes preferred to be in separate burrows rather than together in one burrow, regardless of the relative sizes of the individuals.  We also observed that males were more aggressive towards one another, whereas females demonstrated very little intrasexual aggression.  The remainder of our experiments investigated the interactions between the sexes when 2 males and 1 female were placed in an arena together.  Overall, the female ended up in a burrow with the larger male in the majority of the trials.  Although it is difficult at this time to disentangle the mechanism by which this occurs, it appears that male competition may play a larger role than female choice.  We found that, when given a choice between empty burrow and one occupied by a member of the opposite sex, males will seek the burrow with the female whereas the female chooses her burrowing site randomly.  Regardless of whether male competition and/or female choice is occurring, larger males do appear able to secure more matings with females. 
     
Although a great deal was accomplished last field season, further study is needed to fully understand all of the facets of sexual selection in Megalorchestia californiana.  I plan to return to Friday Harbor Labs next summer ton continue my research, and hopefully bring back some organisms to perform some laboratory experiments as well.  Many behavioral aspects of this mating system remain unknown, so there are many exciting avenues of investigation to explore.
     
     

 

Adelges tsugae (Homoptera: Adelgidae): The Hemlock Woolly Adelgid
 
The hemlock woolly adelgid is a major pest on Eastern hemlocks (Tsuga canadensis), the state tree of Pennsylvania.  The woolly adelgid feeds on the phloem of hemlocks, and can be distinguished by a cotton-like structure where the insect lays its eggs (see picture).  The pest is native to Asia, and was introduced in the western US in the 1920s but did not appear in the eastern US until the 1950s.  Hemlocks in the western US and Asia appear to be more resistant to the adelgid, whereas eastern hemlocks are highly susceptible to injury and have an increased likelihood of mortality when infested by the insect.  Recent work by Dr. Lagalante of Villanova University has shown that there are significant differences in the chemical profiles of eastern hemlocks vs. western (and Asian) hemlocks.  Dr. Lagalante and I are currently collaborating on multiple projects with the hemlock woolly adelgid, including the incorporation of chemicals associated with resistance into eastern hemlocks and the subsequent effects on survivorship and fecundity of the pest.

The life cycle of the hemlock woolly adelgid includes 2 generations per year called the sistens and the progrediens.  Sistens hatch in late June, and the young nymphs (crawlers) search for an appropriate place to insert their stylet before aestivating for the entire summer.  These adelgids break aestivation around mid-October, and proceed to feed at the base of the needle through the leaf cushion. Throughout the winter, they continue to feed and grow, and eventually form the woolly mass in which they lay eggs that will become members of the progredien generation.  In late March or early April, the progredien nymphs (crawlers) hatch and find a suitable place to feed.  The progredien generation proceeds at a rapid pace, as they immediately begin feeding, growing and reproducing - progredien adults lay sisten eggs in late June, and die soon thereafter. 
The crawler phase of the 1st instar is the only stage of the forms of adelgid on hemlock capable of selecting feeding sites - as a result, chemical levels during each generation’s crawler stage may influence settling preferences and survival.  In this regard, the most critical aspect of our experiments will involve observations of the probing behavior, settling and survival of the crawlers on hemlock possessing different chemical levels.  We conjecture that crawlers on unfavorable foliage (i.e., foliage with high levels of infused chemicals) will insert and retract their stylet multiple times before a final insertion, whereas the stylet insertion frequency of crawlers on normal (non-infused) foliage will be less.  Based on the temporal and spatial results of previous studies, we expect the progredien crawlers to be discriminate in their settling preferences given that they have access to both mature, hardened needles and new green growth.  The sisten crawler settles when both old growth and extended, new growth is available but appears to settle preferentially on new growth. In both generations, however, there is potential for the chemical profile to affect the adelgids, as nymphs must remove their stylet bundle while molting.  Molting is then followed by reinsertion, usually in the same place (under normal conditions).  This stylet removal and reinsertion around the time of molting leaves open the possibility that, even after settling, nymphs may move and exhibit behavioral responses to augmented chemical levels.