Month: September 2022

MARINE FOOTPRINT. "Spending weeks in the plankton or metamorphosing into a benthic juvenile within hours since fertilization is clearly a choice on which natural selection has left its footprint in many marine invertebrates." http://rstb.royalsocietypublishing.org/content/365/1540/631.short View in LinkedIn

SCHEDULING SYNCHRONY. "It is of interest that both the switch between alternative developmental routes and the developmental transitions involving major morphological and ecological changes often co-occur within the developmental schedule." http://rstb.royalsocietypublishing.org/content/365/1540/631.short View in LinkedIn

SYNCHRONY EXAMPLE. "We have seen such a coincidence between the phase at which some normal nematode larvae switch to a dauer fate, and the phase during which a free-living larva of other nematodes becomes parasitic." http://rstb.royalsocietypublishing.org/content/365/1540/631.short View in LinkedIn

CONSERVED DEVELOPMENTAL SEQUENCES. "The more the expression of a specific phenotype falls under genetic control, the more it is likely to be expressed. In turn, its expression is likely to facilitate also the expression of other specific phenotypes in conserved developmental sequence." http://rstb.royalsocietypublishing.org/content/365/1540/631.short View in LinkedIn

TEMPORAL SEQUENCES. "In this way, a series of different, sequentially realized alternative phenotypes compatible with the animal's genome, but individually expressed in the presence of different transcription patterns, will gradually evolve towards a strictly controlled temporal sequence of developmental stages." http://rstb.royalsocietypublishing.org/content/365/1540/631.short View in LinkedIn

RARE REVERSIBILITY. "Also, the probability that this sequence will occasionally reverse will probably vanish soon, as demonstrated by the life cycles of most animal species. Exceptions to this rule are indeed extremely rare. Best known is the case of the hydrozoan Turritopsis nutricula, where a medusa, under certain conditions, is able to revert to a polyp." http://rstb.royalsocietypublishing.org/content/365/1540/631.short View in LinkedIn

WHAT-A-SENTENCE. "If an animal's complex life cycle derives from diachronic fixation of the alternative phenotypes originally expressed as polyphenisms, this historical continuity is likely to have left an imprint in the internal mechanisms that mediate the most conspicuous developmental changes, as at metamorphosis." http://rstb.royalsocietypublishing.org/content/365/1540/631.short View in LinkedIn

SWITCH FIXATION. "We can expect that even after genetic fixation of a developmental switch, its expression may still depend on the availability of generic cues. This is what is found in many embryonic and post-embryonic developmental sequences, when examining conspecific larvae exposed to different environmental cues, or through comparisons of the larvae of closely related species." http://rstb.royalsocietypublishing.org/content/365/1540/631.short View in LinkedIn

"LIFE CYCLE COMPLEXIFICATION is likely to originate, preferentially, in a less predictable and less stable, perhaps seasonally changing environment. This is the context where the extensive variation in external conditions is likely to release extensive polyphenic responses." http://rstb.royalsocietypublishing.org/content/365/1540/631.short View in LinkedIn

SO ENDS this section on complex life cycles. As you may surmise, the field is a bit stuck in a Victorian mindset, and needs a good kick in the rear end with deep comparative genomics. The fact remains, it is a curiosity box of strange evolutionary ticks and quirks, a funny farm looking for a cause. Nevertheless, our bespectacled Victorians did do an excellent job of curating their collection of freaks. View in LinkedIn