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Animals with biphasic lifecycles often inhabit different visual environments across ontogeny. Many frogs and toads (Amphibia: Anura) have free-living aquatic larvae (tadpoles) that metamorphose into adults that inhabit a range of aquatic and terrestrial environments. Ecological differences influence eye size across species, but these relationships have not yet been explored across life stages in an ontogenetic allometric context. We examined eye-body size scaling in a species with aquatic larvae and terrestrial adults, the common frog Rana temporaria, using a well-sampled developmental series. We found a shift in ontogenetic allometric trajectory near metamorphosis indicating prioritized growth in tadpole eyes. To explore the effects of different tadpole and adult ecologies on eye-body scaling, we expanded our taxonomic sampling to include developmental series of eleven additional anuran species. Intraspecific eye-body scaling was variable among species, with 8/12 species exhibiting a significant change in allometric slope between tadpoles and adults. Traits categorizing both tadpole ecology (microhabitat, eye position, mouth position) and adult ecology (habitat, activity pattern) across species had significant effects on allometric slopes among tadpoles, but only tadpole eye position had a significant effect among adults. Our study suggests that relative eye growth in the preliminary stages of biphasic anuran ontogenies is somewhat decoupled and may be shaped by both immediate ecological need (i.e. tadpole visual requirements) and what will be advantageous during later adult stages.
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HOW TO BUILD A HECKIN’ CHONKER: BODY INFLATION IN THE ONTOGENY OF CARCINOSOMATID EURYPTERIDS
Understanding how the mechanisms that result in the development of new morphologies act is fundamental to exploring how evolutionoperates. Carcinosomatids are an unusual group of eurypterids which are characterized by the possession of a greatly expanded,disc-like preabdomen along with relatively short prosomal appendages bearing well-developed spines. The ontogeny of this highlydistinctive group is revealed by a species from the Silurian of Lesmahagow, Scotland. Specimens of Carcinosoma scorpioides ,originally considered to be three separate species, are here shown to represent at least three different ontogenetic stages rangingfrom early juveniles to adults. The earliest instars are markedly different from the adults, with a narrow preabdomen and elongatedprosomal appendages bearing moderately-sized spines, resulting in an overall appearance more reminiscent of the closely relatedmixopterids. The species first undergoes an expansion of the preabdomen while a relative reduction in the length of the prosomalappendages occurs in later instars. Other eurypterids exhibit a relative reduction in prosomal appendage length over ontogeny, withjuveniles having exceptionally long appendages, and also have a reduced prosomal armature which increases progressively duringgrowth. Eurypterids also show a positive allometric trend in preabdominal width early in their ontogeny. As such, Carcinosomascorpioides exhibits the same general developmental trends seen in other eurypterids, indicating that the ontogenetic trajectory ofeurypterids is generally conserved even amongst highly aberrant members of the clade. Furthermore, the preserved ontogeny of Carcinosoma scorpioides suggests that the unusual morphology of carcinosomatids developed due to peramorphic heterochronicprocesses whereby species develop exaggerated characteristics along the ontogenetic trajectory beyond the ancestral condition.Interestingly, despite these traits all being derived through peramorphy, mosaicism is evident in these heterochronic changes with thebody width increase occurring due to an increase in the rate of allometric change early on in ontogeny, while the reduced appendagelength and enlarged armature appears to be associated with an increase in body size and may be due to either a delay in reachingmaturity or an increase in the rate of growth later in ontogeny.
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- Award ID(s):
- 1943082
- PAR ID:
- 10582985
- Publisher / Repository:
- Geological Society of America Abstracts with Programs
- Date Published:
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.1130/abs/2024AM-401349
