Heterochronic evolution in the Heliolites interstinctus-decipiens lineage of the Chaleur Bay region, eastern Canada

A study of the Heliolites interstinctus-decipiens lineage from the Silurian of the Chalcur Bay region, eastern Canada, indicates that most morphological characters of this lineage, including tabularium diameter, coenenchymal tubule diameter and corallite spacing, remain relatively invariate through a Llandovery to Pridoli interval of about 20 million years. In contrast, septal development and corallite wall erenulation show pronounced evolutionary changes due to heterochrony, as shown by comparison of astogenies throughout the lineage. The reduction of septa and the replacement of crenulate corallites by smooth ones in the 'decipiens' type descendent appear to have been by paedomorphosis from the 'interstinctus' type ancestor. The problems of speciation in this lineage are discussed including the alternative hypotheses of a speciation event in the early Ludlow or a phyletic trend within a single species whose longevity is due in part to the stabilization processes of niche separation.     

Phenotypic plasticity in hoverflies: the relationship between colour pattern and season in Episyrphus balteatus and other Syrphidae

1. The abdominal colour patterns of some multivoltine species of hoverfly are phenotypically plastic and change through the flying season.
2. It was predicted how the abdominal colour pattern of one species, Episyrphus balteatus , should change in the field with season based on a hypothesis that the pattern influences the thermoregulatory capabilities of the animal. The colour patterns were quantified using image analysis. The observed changes in the colour pattern through the year supported the thermoregulation hypothesis.
3. A further three Metasyrphus species were analysed similarly to allow a comparative study of the forms of the plasticities of the above four species and four Eristalis species from a previous study.
4. Whilst it was clear that the abdominal colour patterns of many of the species were plastic, it was also apparent that not all species used the same developmental pathway to control the seasonal colour pattern changes. This suggests convergent evolution towards a general type of plasticity and that abdominal colour pattern plasticity in hoverflies is functional.