Limits...
When field experiments yield unexpected results: lessons learned from measuring selection in White Sands lizards.

Hardwick KM, Harmon LJ, Hardwick SD, Rosenblum EB - PLoS ONE (2015)

Bottom Line: Color did not have a significant effect on survival, but we found several unexpected relationships including variation in predation over small spatial and temporal scales.In addition, we detected a marginally significant interaction between sex and color, suggesting selection for substrate matching may be stronger for males than females.We use our results as a case study to examine six major challenges frequently encountered in field-based studies of natural selection, and suggest that insight into the complexities of selection often results when experiments turn out differently than expected.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, University of Idaho, Moscow, Idaho, United States of America.

ABSTRACT
Determining the adaptive significance of phenotypic traits is key for understanding evolution and diversification in natural populations. However, evolutionary biologists have an incomplete understanding of how specific traits affect fitness in most populations. The White Sands system provides an opportunity to study the adaptive significance of traits in an experimental context. Blanched color evolved recently in three species of lizards inhabiting the gypsum dunes of White Sands and is likely an adaptation to avoid predation. To determine whether there is a relationship between color and susceptibility to predation in White Sands lizards, we conducted enclosure experiments, quantifying survivorship of Holbrookia maculate exhibiting substrate-matched and substrate-mismatched phenotypes. Lizards in our study experienced strong predation. Color did not have a significant effect on survival, but we found several unexpected relationships including variation in predation over small spatial and temporal scales. In addition, we detected a marginally significant interaction between sex and color, suggesting selection for substrate matching may be stronger for males than females. We use our results as a case study to examine six major challenges frequently encountered in field-based studies of natural selection, and suggest that insight into the complexities of selection often results when experiments turn out differently than expected.

Show MeSH
Proportion of lizards that survived trials with respect to enclosure treatment and paint treatment.Survivorship was significantly lower in the open enclosure treatment than in the closed enclosure treatment (P < 0.05 indicated by an “*”). We did not detect a significant difference in survivorship by paint treatment group. Bars represent mean survivorship across enclosure replicates, and vertical lines indicate the standard error of the mean. The open versus closed enclosure treatment comparison includes data from 2011 trials only (three open and three closed replicates, n = 84 lizards). The matched versus mismatched paint treatment comparison includes data from 2011 and 2012 trials (15 open replicates, n = 210 lizards).
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4340912&req=5

pone.0118560.g002: Proportion of lizards that survived trials with respect to enclosure treatment and paint treatment.Survivorship was significantly lower in the open enclosure treatment than in the closed enclosure treatment (P < 0.05 indicated by an “*”). We did not detect a significant difference in survivorship by paint treatment group. Bars represent mean survivorship across enclosure replicates, and vertical lines indicate the standard error of the mean. The open versus closed enclosure treatment comparison includes data from 2011 trials only (three open and three closed replicates, n = 84 lizards). The matched versus mismatched paint treatment comparison includes data from 2011 and 2012 trials (15 open replicates, n = 210 lizards).

Mentions: Survivorship differed significantly between open and closed treatments in trials conducted in 2011, where survivorship was higher for lizards in closed treatments than in open (Fisher’s exact test, P < 0.01). In fact, 100% of the lizards within the closed treatment group survived, compared with only 36% (95% CI [5%, 67%]) of lizards in the open treatment group (Fig. 2). However, survivorship in open replicates did not differ between paint treatments (χ21 = 0.02, P = 0.89). 36% of lizards in the open treatment survived in 2011, with 38% (95% CI [0%, 100%]) of substrate-matched lizards surviving, and 33% (95% CI [13%, 53%]) of substrate-mismatched lizards surviving. In 2012, 61% (95% CI [42%, 80%]) of lizards survived, with 59% (95% CI [37%, 81%]) of substrate-matched lizards surviving, and 63% (95% CI [46%, 80%]) of substrate-mismatched lizards surviving. Thus for 2011 and 2012 combined, 56% (95% CI [40%, 72%]) of all lizards in the open treatment survived, with 55% (95% CI [36%, 74%]) of substrate-matched lizards surviving and 57% (95% CI [42%, 72%]) of substrate-mismatched lizards surviving (Fig. 2).


When field experiments yield unexpected results: lessons learned from measuring selection in White Sands lizards.

Hardwick KM, Harmon LJ, Hardwick SD, Rosenblum EB - PLoS ONE (2015)

Proportion of lizards that survived trials with respect to enclosure treatment and paint treatment.Survivorship was significantly lower in the open enclosure treatment than in the closed enclosure treatment (P < 0.05 indicated by an “*”). We did not detect a significant difference in survivorship by paint treatment group. Bars represent mean survivorship across enclosure replicates, and vertical lines indicate the standard error of the mean. The open versus closed enclosure treatment comparison includes data from 2011 trials only (three open and three closed replicates, n = 84 lizards). The matched versus mismatched paint treatment comparison includes data from 2011 and 2012 trials (15 open replicates, n = 210 lizards).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4340912&req=5

pone.0118560.g002: Proportion of lizards that survived trials with respect to enclosure treatment and paint treatment.Survivorship was significantly lower in the open enclosure treatment than in the closed enclosure treatment (P < 0.05 indicated by an “*”). We did not detect a significant difference in survivorship by paint treatment group. Bars represent mean survivorship across enclosure replicates, and vertical lines indicate the standard error of the mean. The open versus closed enclosure treatment comparison includes data from 2011 trials only (three open and three closed replicates, n = 84 lizards). The matched versus mismatched paint treatment comparison includes data from 2011 and 2012 trials (15 open replicates, n = 210 lizards).
Mentions: Survivorship differed significantly between open and closed treatments in trials conducted in 2011, where survivorship was higher for lizards in closed treatments than in open (Fisher’s exact test, P < 0.01). In fact, 100% of the lizards within the closed treatment group survived, compared with only 36% (95% CI [5%, 67%]) of lizards in the open treatment group (Fig. 2). However, survivorship in open replicates did not differ between paint treatments (χ21 = 0.02, P = 0.89). 36% of lizards in the open treatment survived in 2011, with 38% (95% CI [0%, 100%]) of substrate-matched lizards surviving, and 33% (95% CI [13%, 53%]) of substrate-mismatched lizards surviving. In 2012, 61% (95% CI [42%, 80%]) of lizards survived, with 59% (95% CI [37%, 81%]) of substrate-matched lizards surviving, and 63% (95% CI [46%, 80%]) of substrate-mismatched lizards surviving. Thus for 2011 and 2012 combined, 56% (95% CI [40%, 72%]) of all lizards in the open treatment survived, with 55% (95% CI [36%, 74%]) of substrate-matched lizards surviving and 57% (95% CI [42%, 72%]) of substrate-mismatched lizards surviving (Fig. 2).

Bottom Line: Color did not have a significant effect on survival, but we found several unexpected relationships including variation in predation over small spatial and temporal scales.In addition, we detected a marginally significant interaction between sex and color, suggesting selection for substrate matching may be stronger for males than females.We use our results as a case study to examine six major challenges frequently encountered in field-based studies of natural selection, and suggest that insight into the complexities of selection often results when experiments turn out differently than expected.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, University of Idaho, Moscow, Idaho, United States of America.

ABSTRACT
Determining the adaptive significance of phenotypic traits is key for understanding evolution and diversification in natural populations. However, evolutionary biologists have an incomplete understanding of how specific traits affect fitness in most populations. The White Sands system provides an opportunity to study the adaptive significance of traits in an experimental context. Blanched color evolved recently in three species of lizards inhabiting the gypsum dunes of White Sands and is likely an adaptation to avoid predation. To determine whether there is a relationship between color and susceptibility to predation in White Sands lizards, we conducted enclosure experiments, quantifying survivorship of Holbrookia maculate exhibiting substrate-matched and substrate-mismatched phenotypes. Lizards in our study experienced strong predation. Color did not have a significant effect on survival, but we found several unexpected relationships including variation in predation over small spatial and temporal scales. In addition, we detected a marginally significant interaction between sex and color, suggesting selection for substrate matching may be stronger for males than females. We use our results as a case study to examine six major challenges frequently encountered in field-based studies of natural selection, and suggest that insight into the complexities of selection often results when experiments turn out differently than expected.

Show MeSH