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Santa Cruz, CA

Vikram Baliga, PhD Candidate at UC Santa Cruz, member of the Mehta Lab. Areas of study: ecology, ontogeny, morphometrics, and comparative methods.

Phylogenetics and Evolutionary Patterns of Cleaning

The maximum clade credibility tree from our Bayesian approach. A single (but very representative) stochastic character map is painted on the phylogeny. Colors correspond to categories of cleaning: orange is juvenile cleaning, green is facultative cleaning, purple is obligate cleaning, and gray is non-cleaning.

The maximum clade credibility tree from our Bayesian approach. A single (but very representative) stochastic character map is painted on the phylogeny. Colors correspond to categories of cleaning: orange is juvenile cleaning, green is facultative cleaning, purple is obligate cleaning, and gray is non-cleaning.

With at least 58 species that exhibit cleaning behavior, the Labridae (wrasses, parrotfishes, and the lesser-known weed whitings) show a tremendous diversity of cleaner fishes. In fact this diversity over 4 times higher than that seen the next highest group: the Gobiidae (14 cleaner species). The diversity of cleaner fishes within a family does not simply scale with the family’s size; for example, the Labridae contain ~631 species, while the Gobiidae have nearly 2000 members.

The staggering species richness of cleaners in the Labridae holds plenty of evolutionary intrigue. Cleaning itself appears to involve a variety of behavioral and morphological adaptations, and thus, one might expect the evolution of cleaning to have relatively few independent origins. In a recent study (Baliga and Law, 2015), we sought to understand how and when cleaning arose in this group.

We used maximum likelihood and Bayesian methods to infer the relationships between 320 species of labrids. Then, using stochastic character mapping, we simulated character histories across the trees we had generated. Our analyses incorporated information for 50 of the 58 species of known cleaners (100% coverage of genera).

From these reconstructions, we inferred that cleaning evolved at least 26-30 times within the Labridae, and that the earliest evolution of cleaning likely occurred 17-21 million years ago. Cleaning appears to be very young: the vast majority of cleaning likely evolved within the last 10 million years.

A conceptual flowcart that illustrates how transitions between states occurred over our reconstructions. The width of each arrow is approximately proportional to how frequent the transition occurred.

A conceptual flowcart that illustrates how transitions between states occurred over our reconstructions. The width of each arrow is approximately proportional to how frequent the transition occurred.

The majority of these events involved transitions from non-cleaners to the juvenile cleaner state. Cleaning in the juvenile phase appears to be a crucial state that bridges other forms of cleaning (facultative and obligate). This underscores the importance of examining juvenile morphology and ontogenetic patterns of morphological change in this rich and diverse system.