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A genetically based ecological trade-off contributes to setting a geographic range limit.

Alexander A Mauro^1,2, Julián Torres-Dowdall³, Craig A Marshall¹

¹Department of Biology, Colorado State University, Fort Collins, Colorado, USA.

Ecology Letters

|October 12, 2021

Summary

The guppy (Poecilia reticulata) stays in freshwater due to competition with Poecilia picta. This interaction limits the guppy's ability to adapt to brackish water environments.

Keywords:

distribution limits euryhaline fish interference competition realised niche salinity translocation experiment/field transplants

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Area of Science:

Ecology
Evolutionary Biology
Ichthyology

Background:

Geographic range limits are shaped by ecological factors and evolutionary constraints.
The guppy (Poecilia reticulata) is euryhaline but restricted to freshwater in its native range.
Understanding range restrictions is crucial for predicting species' responses to environmental change.

Purpose of the Study:

To investigate why Poecilia reticulata is confined to freshwater despite its salinity tolerance.
To test the hypothesis that competitive interactions with Poecilia picta limit P. reticulata's brackish water colonization.
To identify potential evolutionary constraints on adaptive evolution at range limits.

Main Methods:

Field transplant experiments to assess survival and behavior in natural conditions.
Common garden breeding experiments to control for genetic background.
Laboratory behavior experiments to quantify competitive interactions.

Main Results:

Poecilia reticulata exhibits behavioral subordination and reduced survival in brackish water when competing with Poecilia picta.
Field transplants confirmed lower survival of P. reticulata in brackish habitats shared with P. picta.
Genetic correlation analysis revealed a trade-off between growth in brackish water and competitive ability.

Conclusions:

Interspecific competition with Poecilia picta is a key factor limiting Poecilia reticulata's geographic range.
A genetically based trade-off between salinity tolerance and competitive ability constrains adaptive evolution.
Ecological interactions can play a significant role in maintaining species range limits.