Intense selective hunting leads to artificial evolution in horn size

Area of Science:

• Evolutionary biology
• Conservation biology
• Wildlife management

Background:

• Selective harvests, such as trophy hunting, can impose artificial selection pressures on wildlife populations.
• Understanding the evolutionary consequences of such practices is crucial for effective conservation strategies.
• Bighorn sheep (Ovis canadensis) have been subject to trophy hunting targeting large horn size.

Purpose of the Study:

• To investigate the evolutionary impact of intensive trophy hunting on horn size in bighorn sheep.
• To determine if observed changes in horn size are attributable to artificial selection or genetic drift.
• To assess the potential for recovery of horn size through natural selection after hunting pressure is reduced.

Main Methods:

• Analysis of 39 years of phenotypic data on bighorn sheep horn size.
• Statistical modeling to assess trends in genetic values for horn traits in response to 23 years of intense hunting.
• Comparison of traits directly targeted by hunting with genetically correlated and uncorrelated traits.

Main Results:

• A significant decline in the genetic value for male bighorn sheep horn length was observed, consistent with artificial selection.
• The probability of the observed change being due to genetic drift alone was low (9.9%).
• Genetically correlated traits showed weak trends, while an uncorrelated trait (female horn base circumference) showed no trend; horn size decline halted but did not reverse after hunting ceased.

Conclusions:

• Selective trophy hunting demonstrably led to evolutionary changes, reducing horn length in bighorn sheep.
• Natural selection acts slowly to reverse evolutionary changes induced by artificial selection, even after hunting pressure is removed.
• These findings highlight the long-term evolutionary impacts of human-induced selection on wildlife populations.