This week’s BEACON Researchers at Work blog post is by University of Texas at Austin postdoc Tessa Solomon-Lane.
I can trace the beginning of my fascination with social behavior to the summer I was ten. That summer, I started volunteering as a teacher’s aide at an arts-based school for kids with learning and developmental differences. As I gained experience at the camp, the scientist in me started to recognize patterns and ask questions. One observation intrigued me most: seemingly independent of a wide variety of special needs, kids who could interact socially with other campers and adults seemed to have a particular advantage. There was an ease with which these campers moved through their day that we, as educators, struggled to instill in campers who didn’t already have that ability. In the long run, one teacher told me, these socially savvy kids would be fine. Although ‘fine’ is overly simple, and some social skills can be coached, I think there was an important kernel in my early observations that still drives my research today: members of highly social species who can play the social game well are likely to have an advantage.
Field biology beyond the playground. Fast forward to a college semester abroad in Australia when, for the first time, it clicked for me that scientific research was the way to ask and answer my persistent questions about social behavior and why individuals behave the way that they do. What led to this realization? I learned there were fish that changed sex depending on their social environment.
Most of the animals we encounter in our everyday lives —humans, dogs, cats, birds, and even zoo animals—are genetically either male or female. Males typically remain males for their entire lives, and females typically remain female. For many species of fish, however, sex is much more flexible. Females that produce eggs can transform into fully functioning males in just days or weeks (protogynous, sequential hermaphrodite). In species like grouper and clownfish, males can sex change into females (protandrous, sequential hermaphrodite), and there are even species that can change from female to male and back again (bidirectional, sequential hermaphrodite). This transformation can dramatically increase lifetime fitness and involves coordinated changes at multiple biological levels. The first changes occur in the brain and behavior of the sex changer. External morphology, such as coloration and genitalia shape, can also shift. Steroid hormones, particularly androgens and estrogens, are central to the reorganization of the reproductive system. And in the gonad itself, an ovary becomes a testis (or vice versa) through a combination of cell birth and cell death.
Remarkably, this whole transition is socially regulated. In a protogynous species, for example, female to male sex change occurs when a female establishes dominance in a social group. In nature, this might happen if the previous dominant male dies or if an all-female group forms. Within minutes of the social environment becoming permissive to sex change, the behavior of the dominant female changes. She may even take on the male role so rapidly that she performs male reproductive behaviors before she has sperm to release.
Why did sex changing fish set off a light bulb for me? Without a doubt, social behavior is critically important for all of the diverse social species found throughout the animal kingdom, including humans. But here were animals that, over the course of a single lifetime, must generate social behaviors appropriate for a low ranking female, a middle ranking female, a high ranking female, and even a dominant male! How do the fish accomplish this behavioral range and context specificity?
In my doctoral research, I addressed this overarching question by studying the bluebanded goby (Lythrypnus dalli), a bidirectional sex changer. I was fortunate to work in the field on Catalina Island, CA and in the laboratory at Georgia State University with a number of excellent undergraduate researchers, including two field teams I led from Agnes Scott College. Over the course of my dissertation, I formed many different kinds of social groups and watched hours upon hours of social interactions with the goal of understanding which factors affected social behavior and how. I formed social groups of different sizes and sex ratios, with adults and juveniles. Sometimes I selected females that were gravid and ready to lay eggs, gave individuals controlled social experiences, or chose fish with specific levels of aggression. In other experiments, I first implanted steroid hormones or injected neuromodulators, such as corticotropin-releasing factor and arginine vasotocin, into the brain. And like any good behavioral biologist, highly accurate reenactments of the behaviors I observed occasionally make their way into conference presentations and K-12 science outreach activities.
The good, the bad, and the adaptive. There is often an impulse to anthropomorphize animal social behavior and label behaviors as ‘good’ or ‘bad’ depending on their connotations for humans. But gobies are not tiny, underwater humans. Subjective classifications can impede our understanding of behavioral evolution because ‘good’ behaviors may or may not actually increase fitness. Furthermore, the fitness consequences of some behaviors, such as aggression, differ depending on the context and the species. Even the individual expressing the behavior can influence the outcome. In my research, I identified adaptive behaviors and successful individuals by directly measuring a component of fitness: reproductive success. For females, I counted the number of eggs she laid in the male’s nest, which ranged from 55 to 2,200 eggs per clutch. For males, I counted the total number of eggs (from multiple females) that hatched from his nest. The most productive male hatched 4,995 eggs in just 2 weeks! By identifying the strong connections between social behavior and reproductive success in bluebanded goby social groups, my research can provide insight into how these important behaviors evolved.
As a new postdoctoral fellow in the Hofmann Lab (cichlid.biosci.utexas.edu), my goal now is to go into the brain. Although I am no longer studying a sex changer, the African cichlid Astatotilapia burtoni is highly social and expresses fascinating and flexible social behaviors. I am excited to begin investigating how a highly conserved network of brain regions regulates the expression of adaptive, context-specific social behavior.
For more information about Tessa’s work, you can contact her at tksolomonlane at utexas dot edu.