The fiddler crab, Minuca pugnax, follows Bergmann's rule.

David Samuel Johnson,James Nelson,Serina Wittyngham,Bethany Williams,Cynthia Crowley,Katherine Longmire

doi:10.1002/ece3.5883

David Samuel Johnson, James Nelson + Show 4 more

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https://doi.org/10.1002/ece3.5883

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Abstract

Bergmann's rule predicts that organisms at higher latitudes are larger than ones at lower latitudes. Here, we examine the body size pattern of the Atlantic marsh fiddler crab, Minuca pugnax (formerly Uca pugnax), from salt marshes on the east coast of the United States across 12 degrees of latitude. We found that M. pugnax followed Bergmann's rule and that, on average, crab carapace width increased by 0.5 mm per degree of latitude. Minuca pugnax body size also followed the temperature–size rule with body size inversely related to mean water temperature. Because an organism's size influences its impact on an ecosystem, and M. pugnax is an ecosystem engineer that affects marsh functioning, the larger crabs at higher latitudes may have greater per‐capita impacts on salt marshes than the smaller crabs at lower latitudes.

Highlights

One of the best-known patterns in biogeography is Bergmann's rule
To examine hypotheses related to temperature variables, we conducted multiple linear regressions to test the effect of the following predictors on mean, mean maximum, and maximum M. pugnax carapace width: mean annual air temperature, mean annual water temperature, standard deviation of air temperature, and standard deviation of water temperature
We found that the fiddler crab, Minuca pugnax, like many other marine invertebrates, follows Bergmann's rule (Darnell & Darnell, 2018; Ho et al, 2010; Manyak-Davis et al, 2013)

Summary

| INTRODUCTION

One of the best-known patterns in biogeography is Bergmann's rule. It predicts that organisms at higher latitudes are larger than ones at lower latitudes (Bergmann, 1847). Finding that M. pugnax did follow Bergmann's rule, our second goal was to explore the role of temperature in driving the body size patterns for M. pugnax. The first hypothesis we tested is the temperature–size rule, which states that there is an inverse relationship between temperature and body size (i.e., individuals are bigger at lower temperatures) (Atkinson, 1994). Several mechanisms have been proposed to explain the temperature–size rule, including variation in maternal investment, growth rates, and critical size with temperature (Atkinson, 1994; Ghosh et al, 2013; Stelzer, 2002). Because our sampling may bias toward collection of larger individuals, we used the following values of carapace width for analysis: mean, mean maximum, and maximum size. The maximum size is a useful index for estimating the relationship between body size and latitude in case of sampling bias because it looks at the largest individuals within each population (Grosholz & Ruiz, 2003; Kelly et al, 2015)

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Findings

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