As our understanding of the world around us advances, so does our ability to draw distinctions between species. The term “species” traditionally separates organisms that cannot mate to form offspring. With the rise of DNA sequencing technology, the term has evolved to separate organisms that have different sequences in genes that are very similar across all organisms - what makes two organisms different enough to be considered different species is hotly debated. Since the
However, it can be difficult to observe these characteristics in organisms that are very small, like the wasps Dr. Mottern studies. Organisms can also evolve to look similar when they are actually not very closely related in a process called convergent evolution. The similar appearance of unrelated organisms is frequently the result of a shared lifestyle or mimicry to confuse predators, and it is just as likely to confuse taxonomists. Today, taxonomists use both physical observations and DNA sequencing to try to identify new species and correct taxonomic mistakes of the past. Dr. Mottern described one such taxonomic revision during his seminar that began as a disagreement between two researchers at University of California (UC), Riverside.
Both researchers believed they had sampled the same species, Cales noacki, at the UC Riverside Biological Control Grove, yet the two sets of DNA data did not agree. While the two researchers were attacking the molecular biology skills of the other, Dr. Mottern stepped in to help prove they were both right: what if two species of wasp had been masquerading as a single species? To answer this question, Dr. Mottern needed the thing every taxonomist needs: more samples. As a result, he placed a the call for an assortment of wasp species in the genus Cales using this charming ‘wanted poster’ at an entomology meeting (Fig 1).
He was overwhelmed with the response. Suddenly, he had Cales samples pouring in from scientists all over the world (Fig. 2). Before his humble call, the majority of Cales samples were from Costa Rica. This is not by chance; Dr. John Noyes was a wasp researcher who frequently visited and swung his net in Costa Rica resulting in an over-abundance of Costa Rican wasp samples. This “Noyes effect” biases the sampling of many groups of small wasps, which makes it difficult to determine the signal from the “Noyes” when determining their worldwide distribution and diversity; the original Cales noacki was itself first described from Brazil, but most of the C. noacki specimens used for biological control were originally imported from Chile. However, other “C. noacki” specimens were collected in a variety of locations in South America. Dr. Mottern used the samples sent to him, plus slide-mounted
Since these wasps were visually indistinguishable, Dr. Mottern had to rely on the darkest of magical arts, math, to distinguish them. By geometrically analyzing the fine differences in the shape of the wings (using a method called Procrustes analysis), Dr. Mottern found that the mysterious Cales rosei was most similar to a shipment from Argentina.
This is where the line between two species of wasp, happily parasitizing whiteflies in the Biological Control Grove at UC Riverside, has been drawn (for now at least). After resolving this dispute, Dr. Mottern has since turned his taxonomic attention to other groups of tiny wasps: Coccobius species (parasitoids of armored scale) and Oobius species (egg parasitoids of beetles, including emerald ash borer).
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About the authors:
Brian Lovett is a PhD student in Dr. Raymond St. Leger’s Lab studying mycology and genetics in agricultural and vector biology systems. He is currently working on projects analyzing mycorrhizal interactions in agricultural systems, the transcriptomics of malaria vector mosquitoes, and the genomes of entomopathogenic fungi.
Mengyao Chen is a Master’s student in Dr. Leslie Pick’s Lab. Her research focuses on segmentation genes in Brown Marmorated Stink Bug (BMSB, Halyomorpha halys). Her current work is looking for orthologs of pair-rule genes in BMSB, and studying their expression and functions using in situ hybridization and RNAi.