The embryonic development of the centipede Strigamia maritima

Abstract

The geophilomorph centipede Strigamia maritima is an emerging model for studies of development and evolution among the myriapods. A draft genome sequence has recently been completed, making it also an important reference for comparative genomics, and for studies of myriapod physiology more generally. Here we present the first detailed description of myriapod development using modern techniques. We describe a timeline for embryonic development, with a detailed staging system based on photographs of live eggs and fixed embryos. We show that the early, cleavage and nuclear migration, stages of development are remarkably prolonged, accounting for nearly half of the total developmental period (approx 22 of 48 days at 13 °C). Towards the end of this period, cleavage cells migrate to the egg periphery to generate a uniform blastoderm. Asymmetry quickly becomes apparent as cells in the anterior half of the egg condense ventrally to form the presumptive head. Five anterior segments, the mandibular to the first leg-bearing segment (1st LBS) become clearly visible through the chorion almost simultaneously. Then, after a short pause, the next 35 leg-bearing segments appear at a uniform rate of 1 segment every 3.2 h (at 13 °C). Segment addition then slows to a halt with 40-45 LBS, shortly before the dramatic movements of germ band flexure, when the left and right halves of the embryo separate and the embryo folds deeply into the yolk. After flexure, segment morphogenesis and organogenesis proceed for a further 10 days, before the egg hatches. The last few leg-bearing segments are added during this period, much more slowly, at a rate of 1-2 segments/day. The last leg-bearing segment is fully defined only after apolysis of the embryonic cuticle, so that at hatching the embryo displays the final adult number of leg-bearing segments (typically 47-49 in our population).

Changing cell behaviours during beetle embryogenesis correlates with slowing of segmentation

“…centipedes, temporal variation is linked to a switch between a mechanism that counts with a two segment periodicity to one which generates single segments 16 . Recently published work 51 suggests the terminal Tribolium segments may also switch from a pair-rule patterning mechanism to an unknown mechanism that generated single segments.…”

“…Support for a clock includes a clear demonstration of molecular oscillations in the flour beetle, Trobolium casteneum 14 . However, species-specific rates of segment addition or variations in those rates are not wellcharacterized among arthropods, with a few exceptions 15,16 .…”

Evolutionary crossroads in developmental biology: the spiderParasteatoda tepidariorum

“…1), in which it was shown that gastrulation takes place along a ventral gastral groove, without the formation of a cumulus (Mayer and Whitington, 2009). Therefore, although the existence of a cumulus in myriapods continues to be unresolved (Brena and Akam, 2011), currently the most parsimonious explanation is that the cumulus evolved after the chelicerate-mandibulate split. However, as a migrating cumulus has also been described in a horseshoe crab (a marine group of chelicerates) (Sekiguchi, 1973), it is likely that this mode of development evolved very early in the chelicerate lineage (Redkin et al, 2008).…”

The embryoid development of Strigamia maritimaand its bearing on post-embryonic segmentation of geophilomorph centipedes

“…Indeed, it is clear that at hatching, a geophilomorph centipede is little more than an embryo without an egg shell, still brooded by the mother for an additional long period. In this animal, the rupture of the egg chorion does not represent a clear-cut change from an embryonic to a post-embryonic state [5,6]. These nonfeeding post-embryonic stages reside with the mother, who stays coiled around them in the brood chamber, a small cavity in the soil matrix.…”

“…This analysis follows up published work on the embryonic development of Strigamia maritima where we have defined, described and timed the several stages [6]. Following a rather traditional approach, in this paper I will use a moult, or more precisely an ecdysis, i.e.…”