Adaptation Generates Extraordinary Diversity In A Tropical Rainforest Fish

by techlowdown · 26 April 2023

Lessons learned from one wildly variable species of fish may teach us how to more effectively conserve tropical rainforests

An international team of scientists recently led a detailed study of eastern rainbowfish, Melanotaenia splendida splendida, a freshwater species that is popular in the aquarium trade. Eastern rainbowfish are common and widespread in the wet tropical rainforests of Queensland’s far north. These fish, often known as the splendid rainbowfish, are notable because they extremely variable, having adapted to local conditions in the creeks and rivers where they live.

How did such a riot of variation in different colors and shapes arise in just one species? Well, it’s complicated.

“We found that, while limited connectivity among different river catchments could explain some of the genetic differences, environmental factors like water flow and temperature offered a better explanation for the patterns overall”, lead author, molecular ecologist Katie Gates, who now is a postdoctoral research fellow at Flinders University, said in a statement.

Typical rainforest stream habitat in northern Queensland where splendid rainbowfish live. (Credit: … [+] Keith Martin.)

Keith Martin

“Tropical rainforests are home to a staggering variety of plants and animals, ranking them among Earth’s greatest biodiversity hotspots”, Dr Gates pointed out. But tropical rainforests are surprisingly poorly studied.

Dr Gates designed her studies to begin addressing this knowledge deficit by studying the links between genomic and environmental variation and the resulting responses in one highly variable species, the splendid rainbowfish. Dr Gates’ ultimate goal was to increase scientific understanding of the genetic basis for adaptation to fluctuating environments, with a particular focus on climate change.

“We need to understand this diversity to prepare for any acceleration in habitat change under climate change and other forces”, Dr Gates said.

Holding an eastern rainbow fish (Melanotaenia splendida splendida), a colorful freshwater fish … [+] popular in aquarium trade, native to small streams in wet tropical rainforests of the far north in Queensland, Australia.

getty

To do this work, Dr Gates and her collaborators captured wild splendid rainbowfish from nine rainforest creek sites across five drainages in the Wet Tropics of Queensland in northeastern Australia. Sampling sites were chosen to maximize representation of rainbowfish variants from across their climatic habitat gradient.

Dr Gates and her collaborators obtained DNA from the fish and carefully measured their body shapes, or morphology (Figure 2). Analysis revealed a clear association between both genetic and morphologic variations and the drainage divisions where these fish live, indicating that limitations of gene flow strongly influences population differences.

F I G U R E 2 | UPPER: The 18 landmarks used for geometric morphometric analysis of the eastern … [+] rainbowfish Melanotaenia splendida splendida. 1: Anterior tip of head, where premaxillary bones articulate at midline; 2: Posterior tip of maxilla; 3: Anterior margin in maximum eye width; 4: Posterior margin in maximum eye width; 5: Dorsal margin of head at beginning of scales; 6: Ventral margin at the end of the head; 7: Dorsal insertion of pectoral fin; 8: Anterior insertion of the pelvic fin; 9: Anterior insertion of the anal fin; 10: Anterior insertion of the first dorsal fin; 11: Posterior insertion of the first dorsal fin; 12: Anterior insertion of the second dorsal fin; 13: Posterior insertion of the second dorsal fin; 14: Posterior insertion of the anal fin; 15: Dorsal insertion of the caudal fin; 16: Posterior margin of the caudal peduncle (at tip of lateral line); 17: Ventral insertion of the caudal fin; 18: Posterior margin of the caudal fin between dorsal and ventral lobes. LOWER: Fig. 4. Wireframe graphical representation of significant principal components of body shape variation based on 18 landmarks for 207 Melanotaenia splendida splendida individuals sampled across nine rainforest sampling localities in the Wet Tropics of Queensland. Dark and light blue frames respectively represent body shapes at high and low extremes of each significant axis (scale factor = 0.75). (doi:10.1038/s41437-023-00612-x)

doi:10.1038/s41437-023-00612-x

The study also showed that water flow differences and other hydrological and thermal variables were important environmental predictors of both genetic and morphological variation. Thus, it’s likely that future changes in water flow and temperature due to climate change could have big impacts on the fitness and diversity of rainbowfish.

Dr Gates and her collaborators’ motivation to better understand how genetics, morphology, and ecology interact to shape the diversity of splendid rainbowfish and apply that knowledge to developing more effective conservation strategies to deal with the unique climate challenges in tropical rainforest ecosystems.

Source:

Katie Gates, Jonathan Sandoval-Castillo, Chris J. Brauer, Peter J. Unmack, Martin Laporte, Louis Bernatchez and Luciano B. Beheregaray (2023). Environmental selection, rather than neutral processes, best explain regional patterns of diversity in a tropical rainforest fish, Heredity | doi:10.1038/s41437-023-00612-x

SHA-256: 9ab94921e06b203a216cb219d873f92ea4083642075e2e0be632939cd42949aa