Population biology of parasitoids

We study the spatial population dynamics of closely interacting species in a fragmented landscape.  This work is rooted in: (1) long-term monitoring of the butterfly Melitaea cinixa and its parasitoids in the Åland islands, (2) detailed study of the behavior and natural history of individual species, and (3) population genetics tools. We have shown that parasitoid metapopulation dynamics are influenced by host dynamics and habitat connectivity, as well as host plant species, hyperparasitism, competition, temperature mediated phenology, and more recently a plant pathogenic fungus.

Three current projects are:

1) Population genetic structure

The population structure of a species depends on the distribution of its resources, its population size and the extent to which individuals move between resource patches. We are using population genetics tools (primarily neutral microsatellite markers) to characterize the population genetic structures of the butterfly M. cinxia and its parasitoids in a landscape, and then exploring the association of that structure with aspects of the environment (such a habitat connectivity), resource distribution (host population dynamics), life history (i.e. population size and sex ratio), and interactions such as competition.

One clear result is that higher trophic level species have lower spatial genetic structure.  This is not surprising because as trophic level increases the resource becomes sparse and unpredictable, so individuals must be mobile, leading to population mixing.

 

Multilocus genetic clusters for each species mapped onto the map of the Åland islands

Relevant papers:

Nair, A., Fountain, T., Ikonen, S., Ojanen, S. P., van Nouhuys, S. 2016. Spatial and temporal genetic structure at the fourth trophic level in a fragmented landscape. Proceedings of the Royal Society B, 283: 10.1098/rspb.2016.0668

Couchoux,, C., Seppä, P., van Nouhuys,, S. 2016. Strong dispersal in a parasitoid wasp overwhelms habitat fragmentation and host population dynamics.  Molecular Ecology, , doi: 10.1111/mec.13696

van Nouhuys, S. 2016.  Diversity, population structure and individual behavior of parasitoids as seen using molecular markers. Current opinions in Insect Science 14: 94-99.

Couchoux, C., Seppä, P., van Nouhuys, S. 2015. Microsatellites for the parasitoid wasp Hyposoter horticola. Conservation Genetics Resources, 7: 595-597 

Nair, A., van Nouhuys, S. 2015. Microsatellite markers for a hyperparasitoid wasp from a fragmented landscape. Conservation Genetics Resources, 7: 565-586

Kankare, M., van Nouhuys, S., Gaggiotti, O., Hanski, I. 2005. Metapopulation genetic structure of two coexisting parasitoids of the Glanville fritillary butterfly. Oecologia, 143: 77-84

2) Intraspecific competition

Generally population biologists and behavioral ecologists think of foraging behavior of parasitoids as related to their ability to find and hosts.  And, we think of rate of parasitism as a result of host accessibility, leading to a density dependent relationship between hosts and parasitoids, with low parasitism at low host density and high parasitism at high host density. But another important aspect of host use by parasitoids is intraspecific competition.  Parasitoids can be very good at finding hosts, so that the success of an individual is more related to its competitive ability than its host finding ability. 

The parasitoid Hyposoter horticola, suffers very strong intraspecific competition for hosts.  Thus quite a lot of the behavior of adult females can be traced to competitive interactions.  Currently we are studying how strength of competition influences the monitoring of potential host egg clusters, and apparent guarding behavior.  We are also studying how rate of parasitism differs (or doesn’t) with strength of competition for hosts, according to an optimal foraging model. To understand competition at realistic spatial and temporal scales we work at a landscape scale.

Relevant papers:

Montovan, K. J., Couchoux, C., Jones, L. E., Reeve, H. K., van Nouhuys, S. The puzzle of partial resource use by a parasitoid wasp. The American Naturalist, 185: 538–550

Couchoux, C. and van Nouhuys, S. 2014. Effects of intraspecific competition and host-parasitoid developmental timing on foraging behaviour of a parasitoid wasp. Journal of Insect Behavior 27: 283-301

Kraft, T. S. and van Nouhuys, S. 2013. The effect of multi-species host density on superparasitism and sex ratio in a gregarious parasitoid. Ecological Entomology 38: 138-146

Corley, J. C., Villacide, J. M., van Nouhuys, S. 2010. Patch time allocation by a parasitoid: the influence of con-specifics, host abundance and distance to the patch. Joural of Insect Behavior, 23: 431-440 

van Nouhuys, S. and Kaartinen, R. 2008. A parasitoid wasp uses landmarks while monitoring potential resources. Proceedings of the Royal Society B, 275: 377-385

van Nouhuys, S, and Ehrnsten, J. 2004. Parasitoid behavior that leads to uniform parasitism of a host available only a few hours per year. Behavioral Ecology, 15: 661-665

3) Sex ratio variation in parasitoid populations

Parasitoid populations can differ in sex ratio (proportion of individuals male) because female Hymenoptera (ants bees and wasps) can control the sex of each egg that is laid. Local mate competition predicts that if individuals mate locally then a mother should produce as few males as possible to assure that her daughters are mated. We predict that for some parasitoids, population size and connectivity affect parasitoid sex ratio such that the fraction male will decrease with decreasing host population size and connectivity. This is because in small and isolated populations most progeny will only have close relatives around to mate with. We expect the effect of habitat isolation to be weak for H. horticola because it is mobile and mating is delayed, and stronger for C. melitaearum which is less mobile and has been observed to sib mate, and M. stigmaticus because it is at a high trophic level so experiences a more fragmented landscape. We are using field survey and a large-scale field experiment to test these predictions.

Relevant papers:

Kraft, T. S. and van Nouhuys, S. 2013 The effect of multi-species host density on superparasitism and sex ratio in a gregarious parasitoid. Ecological Entomology 38: 138-146

van Nouhuys, S. and Laine, A-L. 2008 Population dynamics and sex ratio of a parasitoid altered by fungal infected diet of host butterfly. Proceedings of the Royal Society B 275: 377-385

Fox L. R., D. K. Letourneau, J. Eisenbach & S. van Nouhuys. 1990 Parasitism rate and sex ratios of a parasitoid wasp: Effects of herbivore and plant quality Oecologia, 83: 414-419

 

Other relevant papers on parasitoid population biology:

van Nouhuys, Saskya (2016) 
Metapopulation Ecology.  In: eLS. John Wiley & Sons, Ltd: Chichester. DOI: 10.1002/9780470015902.a0021905.pub2

Hajek, A. E. and van Nouhuys, S.  2016
Fatal diseases and parasitoids: from competition to facilitation in a shared host.
Proceedings of the Royal Society B, in press

Duplouy, A., Couchoux, C., Hanski, I., van Nouhuys, S. 2015. Wolbachia infection in a natural parasitoid wasp population. PLOS One, 10(8): e0134843. doi:10.1371/journal.pone.0134843

van Nouhuys, S. and Punju, E. 2010. Coexistence of competing parasitoids: which is the fugitive and where does it hide? Oikos, 119: 61-70

van Nouhuys, S. and Laine, A-L. 2008. Population dynamics and sex ratio of a parasitoid altered by fungal infected diet of host butterfly. Proceedings of the Royal Society B, 275: 787-795

Elzinga, J. A., van Nouhuys, S., van Leeuwen, D. J., Biere, A. 2007. Distribution and colonization ability of three parasitoids and their herbivorous host in a fragmented landscape. Basic and Applied Ecology, 8: 75-88

Kankare, M., van Nouhuys, S., Gaggiotti, O., Hanski, I. 2005. Metapopulation genetic structure of two coexisting parasitoids of the Glanville fritillary butterfly. Oecologia, 143: 77-84

van Nouhuys, S. 2005. Effects of habitat fragmentation at different trophic levels in insect communities. Annales Zoologici Fennici, 42: 433-447

van Nouhuys, S., & G. C. Lei. 2004. Parasitoid and host metapopulation dynamics: the influence of temperature mediated phenological asynchrony. Journal of Animal Ecology, 73: 526-535

van Nouhuys, S., & I. Hanski. 2002. Colonization rates and distances of a host butterfly and two specific parasitoids in a fragmented landscape. Journal of Animal Ecology, 71: 639-650

van Nouhuys, S. & W.T. Tay. 2001. Causes and consequences of small population size for a specialist parasitoid wasp. Oecologia, 128: 126-133

van Nouhuys, S. & I. Hanski. 1999. Host diet affects extinctions and colonizations in a parasitoid metapopulation. Journal of Animal Ecology, 68: 1248-1258