Hierarchical (mm- to km-scale) environmental variation affecting skeletal phenotype of a marine invertebrate (Electra pilosa, Bryozoa): Implications for fossil species concepts

A comparative record of morphological change of fossil specimens through geologic time can provide insights into the rates and patterns of microevolution and speciation. However, questions concerning the extent to which environmental conditions influence skeletal morphology, and potentially confound recognition of genetic change, can be most meaningfully addressed with living taxa. The marine encrusting blyozoan, Electra pilosa (L), was used to assess the magnitude of environmental effects on zooecium-level skeletal morphology at different spatial scales. The latter included environmental effects or factors ranging in level from (1) micro-environmental (variation within and among immediately adjacent colonies), (2) meso-environmental (small-scale colony positional effects among colonies within a common habitat), and (3) macro-environmental (morphological variation among colonies from recognizably different environmental settings).

Macro-environmental influence on zooecial morphology for colonies among localities (10 km-scale) can be detected by comparison of colonies from wave-protected/tidal-dominated versus open coast/wave-dominated settings, and this accounted for similar to 75% of the observed morphological variation. Meso-environmental variation that is, small-scale (10(1) to 10(2) m) systematic (nonrandom) differences that would go undetected in a geologic setting - had a minimal deterministic influence on zooecial morphology, and accounted for similar to 2.5% of observed variation.

Variation among colonies from the same site was highly significant. Much of this morphologic variation (similar to 30%) is attributable to genotypic variation among colonies, but micro-environmental sources cannot be excluded (10(1) to 10(2) cm-scale). Variation within colonies, accounting for similar to 60% of the observed morphological variation, can be further partitioned into Micro-environmental differences, similar to 40% (10(1) to 10(2) mm-scale) associated with spatiotemporal position, and the Life History of individual modules (similar to 20%). Environmental levels (factors) that are associated with significant morphological effects can also be recognized by their sedimentological properties, which can be preserved in the geologic record. Thus, results from this and similar studies have relevance for and can potentially be directly applied to studies of fossil organisms.