RESEARCH:

Research projects in the lab are diverse and include studies of the evolution of body form of closely related fishes adapting to different habitats, the impact of human-mediated habitat transformation on fishes, and the evolutionary history and population genetic structure of Neotropical fish species. A major focus of the lab involves studying how the axial skeleton responds to the evolution of body form as populations adapt to different habitats, the functional significance of these changes, and the underlying developmental mechanisms. The lab is also conducting basic research on the ecology and evolution of freshwater fish species in western Ecuador.

A few ongoing projects in the lab are highlighted below.


Adaptive evolution and speciation along elevational gradients of the Andes Mountains in the genus Rhoadsia (Characidae: Rhoadsiinae):


Rhoadsia is a genus in the family Characidae (tetras) that is endemic to western Ecuador and northwestern Peru. It is characterized by having a very deep body, a large black spot towards the center of the body, and displaying extreme sexual dimorphism. Males grow larger than females and develop bright red and irredescent breeding colors as well as extremely elongate dorsal and anal fin rays. There are two recognized species in the genus, R. altipinna, described from lower elevations in southwestern Ecuador, and R. minor, described from high elevations (>1200 m) from northwestern Ecuador in the Esmeraldas River drainage. Although there are some minor differences between them in morphology, especially in body shape (R. altipinna is deeper bodied than R. minor), their status as distinct species has been questioned (e.g., Gery, 1977). It is now clear that R. altipinna can occur to at least 1100 m in southwestern Ecuador (Jubones drainage) and R. minor occurs to almost sea-level in the Esmeraldas drainage, thus the elevational distriubutions of the two species broadly overlap (Malato et al., 2017). Their body shape also changes with elevation within drainages. Although R. minor at high elevations of the Esmerladas drainage is much more extreme, body shape becomes more streamlined with elevation in both species in three rivers that have been examined to date (Aguirre et al., 2016; Malato et al. 2017).


Fig. 1. A. Male (top) and female (bottom) Rhoadsia altipinna from southwestern Ecuador. B. Depiction of body shape variation with elevation in Rhoadsia based on Malato et al. (2017).

Our lab is currently expanding our research and conducting a phylogeographic analysis to better understand the relationships of populations throughout western Ecuador and determine whether there is genetic evidence for one, two, or more species. More broadly, we are interested in understanding the factors causing the correlation between body shape and elevation in this genus, as well as its genetic and developmental basis.


Temperature effects on somitogenesis, body shape, and the development of the axial skeleton in Astyanax mexicanus:


The Characidae (tetras) are the most diverse family of freshwater fishes in the Neotropics. Our lab is interested in understanding the role that environmental variation during development has on the production of phenotypic variation in characids, and how this in turn may influence the evolutionary trajectory of species adapting to new or changing habitat conditions. We are particularly interested in the impact of temperature because few factors have a greater influence on the phenotypic properties of ectotherms and because of the growing environmental problems associated with global climate change. Temperature variation during embryogenesis is also known to impact adaptively important traits like vertebral number and body shape, which has important fitness consequences.


Fig. 2. A. Effects of temperature on growth of Astyanax mexicanus. Siblings 22 days old grown at 20 (top), 24 (middle) and 28 (bottom) degrees celsius. B. Radiograph of a specimen of A. mexicanus. Numbers indicate individual vertebrae not counting the webberian apparatus or the urostyle. C. Confocal microscopy image of an A. mexicanus embryo stained with Dapi.

We are conducting lab experiments on the emerging model species Astyanax mexicanus to study the effects of temperature variation during development on somite formation, the timing and pattern of bone formation in the axial skeleton, and overall body shape. We are particularly interested in the relationship between the direction of phenotypic change under lab conditions and the patterns of divergence seen among populations and species in nature. Understanding the developmental basis of the phenotypic changes documented is a major direction of future research.


The ecology and evolution of the freshwater fishes of western Ecuador:


Our lab also maintains an active research program studying general aspects of the ecology and evolution of the freshwater fishes of western Ecuador. Western Ecuador is not a region of high species diversity but rates of freshwater fish endemism are among the highest in South America. Unfortunately, fishes in the region are also under severe pressure from habitat destruction and degradation, pollution from agriculture, mining, and human settlements, overexploitation, dam construction, etc. Very little is known about the ecology or evolution of most species and new species are still being described. Our lab is contributing to filling in gaps in knowledge of the fishes in the region. To do so, we maintain a web page summarizing information on the fishes of western Ecuador:

http://condor.depaul.edu/waguirre/fishwestec/

We have contributed to the first field guide on the fishes of western Ecuador:

-Jiménez Prado, P., W. Aguirre, E. Laaz Moncayo, R. Navarrete Amaya, F. Nugra Salazar, E. Rebolledo Monsalve, E. Zárate Hugo, A. Torres Noboa, J. Valdiviezo Rivera. 2015. Guía de Peces para Aguas Continentales en la Vertiente Occidental del Ecuador. PUCESE, UDA and MECN, Esmeraldas, Ecuador, 416 pp.

We are also conducting multiple studies on the fishes in the region.



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