Bones in motion: Ontogeny of craniofacial development in sympatric arctic charr morphs

Abstract

Background: The impressive diversity in the feeding apparatus often seen among related fish species clearly reflects differences in feeding modes and habitat utilization. Such variation can also be found within species. One example of such intraspecific diversity is the Arctic charr in Lake Thingvallavatn, where four distinct morphs coexist: two limnetic, with evenly protruding jaws, and two benthic, with subterminal lower jaws. We used these recently evolved morphs to study the role of ontogenetic variation in shaping craniofacial diversity. Results: The segmental development of the pharyngeal arches and the order of events in craniofacial development is the same as has been described for teleosts, emphasizing the conserved nature of this process. However, our morphometric analyses reveal differences between morphs. Hatching is accompanied by increase in size and allometric shape changes in Arctic charr. Ontogenetic trajectories of craniofacial shape also differ significantly between morphs. Conclusions: The results point to hatching as a significant developmental event in Arctic charr and possibly other fishes. Also, the developmental origins of limnetic and benthic specializations in the craniofacial elements of Arctic charr may stem from events around hatching. This calls for investigations of the mechanisms and consequences of hatching, in the context of development and evolution.

The developmental transcriptome of contrasting Arctic charr (Salvelinus alpinus) morphs

“…Our new data also demonstrate differences in craniofacial elements between AC- and SB-charr, along a limnetic vs. benthic axis 79 . Based on those differences between benthic and limnetic charr, we investigated further genes with roles in craniofacial development that were differentially expressed in the transcriptome.…”

“…We focused on genes with known craniofacial expression in zebrafish development 77 and compared two benthic (SB, LB) and two limnetic charr (AC, PL). We analyzed heads at three time-points (178, 200 and 218 τs ) as this period overlaps with early stages of craniofacial skeletal formation in Arctic charr 78, 79 . The qPCR confirmed the higher expression of seven out of these eight genes in the head of benthic charr compared to limnetic charr ( Figure 5, S2 Figure and S3 file).…”

A way forward with eco evo devo: an extended theory of resource polymorphism with postglacial fishes as model systems

“…Arctic charr provide a classic example of resource polymorphism with the occurrence of multiple morphs that differ in trophic morphology and size associated with resource use. Developmental studies show that differences in head and jaw shape among morphs emerge during embryonic development (Skúlason et al, 1989a;Ahi et al, 2015;Kapralova et al, 2015;Guðbrandsson et al, 2018), correlate with variable timing of bone ossification (Eiríksson et al, 1999) and are effected by diet (Parsons et al, 2011), i.e. evo devo and eco devo processes.…”

Gene expression in the phenotypically plastic Arctic charr (Salvelinus alpinus): A focus on growth and ossification at early stages of development

“…Due to their large size, FF individuals were decapitated behind the pectoral fin and RNA extracted from the head and body separately. However, only the head was included in this study as much of the phenotypic variation in Arctic charr is associated with trophic morphology, as well as large body size being reflected by large head size (Kapralova et al, 2015).…”

“…In this vain, Ahi et al () found gene expression networks that are associated with craniofacial divergence in developing heads of benthic and pelagic Arctic charr morphs. This gene expression variation is also reflected − to some extent − in morphology (Kapralova et al, ), and could explain variable timing of ossification during embryonic development in the offspring of benthic and pelagic morphs of Arctic charr (Eiríksson, Skúlason, & Snorrason, ).…”