Why might they be giants? Towards an understanding of polar gigantism

Abstract

SummaryBeginning with the earliest expeditions to the poles, over 100years ago, scientists have compiled an impressive list of polar taxa whose body sizes are unusually large. This phenomenon has become known as ʻpolar gigantismʼ. In the intervening years, biologists have proposed a multitude of hypotheses to explain polar gigantism. These hypotheses run the gamut from invoking release from physical and physiological constraints, to systematic changes in developmental trajectories, to community-level outcomes of broader ecological and evolutionary processes. Here we review polar gigantism and emphasize two main problems. The first is to determine the true strength and generality of this pattern: how prevalent is polar gigantism across taxonomic units? Despite many published descriptions of polar giants, we still have a poor grasp of whether these species are unusual outliers or represent more systematic shifts in distributions of body size. Indeed, current data indicate that some groups show gigantism at the poles whereas others show nanism. The second problem is to identify underlying mechanisms or processes that could drive taxa, or even just allow them, to evolve especially large body size. The contenders are diverse and no clear winner has yet emerged. Distinguishing among the contenders will require better sampling of taxa in both temperate and polar waters and sustained efforts by comparative physiologists and evolutionary ecologists in a strongly comparative framework.

Algal pigments in Southern Ocean abyssal foraminiferans indicate pelagobenthic coupling

“…We have no explanation for this particular phenomenon but gigantism has been described in other organisms from the deep Southern Ocean (Moran and Woods, 2012). Most foraminiferans in Fig.…”

Estructurada de las comunidades bontónicas en tres sitios de las islas Shetland del sur (Antártida): Patrones de diversidad, composición y tamaños corporales

“…Aunque existe fuerte evidencia a favor para determinados grupos (Moran & Woods, 2012), lo cierto es que es una característica que debe ser evaluada minuciosamente dentro de determinados grupos taxonómicos y resulta necesario extrapolar esos datos con aquellos provenientes de otras partes del mundo para determinar la veracidad y alcance de este patrón. Los histogramas realizados en este estudio, en donde se evalúa la relación entre la abundancia y biomasa, no resultaron contundentes para identificar casos de enanismo y gigantismo.…”

“…Aunque no existe una definición universal del gigantismo polar, la evidencia comparativa es fuerte, al menos para algunos grupos taxonómicos como copépodos, pterópodos, cefalópodos ctenóforos, quetognatos, foraminíferos, anfípodos, isópodos, esponjas, anélidos, equinodermos y picnogónidos; por el contrario, otros grupos tienden hacia el enanismo, como los bivalvos, escafópodos, quitones, peces, braquiópodos y gasterópodos prosobranquios (Moran & Woods, 2012). En este sentido, el frío extremo y constante de los ambientes marinos polares ha sido implicado en muchas características inusuales, como el gigantismo mencionado.…”

“…En este sentido, el frío extremo y constante de los ambientes marinos polares ha sido implicado en muchas características inusuales, como el gigantismo mencionado. Este fenómeno posiblemente es el más complejo de resolver debido a que el tamaño corporal es central para los procesos ecológicos y evolutivos (Moran & Woods, 2012).…”

Distribution and reproduction of the Arctic ctenophore Mertensia ovum in the Baltic Sea

“…Also animals (including ctenophores) living in polar regions grow larger compared to their conspecifics in warmer and more shallow waters (e.g. see Moran & Woods 2012 for review). These differences in ctenophore body size, between the polar and temperate regions, will likewise have an influence on other life history traits, such as egg size, size at first reproduction, and metabolic rates.…”