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The coffin fly, Megaselia scalaris, is a species ofmedical and forensic importance and is increasingly being used for the study of genetics. Postmortem interval can be estimated based on the life stage of M. scalaris recovered from corpses, therefore many studies have addressed the duration of each life stage. These studies demonstrate that embryogenesis completes significantly faster in M. scalaris than in the congener Megaselia abdita and faster even than the 24 hours needed for Drosophila melanogaster embryogenesis. However, until now it has been unclear if this increased speed is achieved by reducing developmental time across all embryonic stages or by the acceleration of individual stages and processes. Here I use time-lapse imaging to create a staging scheme for M. scalaris embryogenesis. Comparison of stages between D. melanogaster and both Megaselia species reveals that heterochronic shifts, simultaneous morphogenetic movements and compression of individual stages all contribute to the rapid development of M. scalaris.
Changes have been made to this version following peer review for the journal Arthropod Structure and Development.
Supporting File S1. Timing of developmental events from individual time-lapse movies in M. scalaris
Stages and developmental events are shown in columns A, B, AC and AD. The green-headed columns and the blue-headed columns indicate developmental timing for D. melanogaster (Campos-Ortega and Hartenstein, 1997) and M. abdita (Wotton et al., 2014) respectively. Orange headed columns indicate M. scalaris data. Time-lapse IDs are listed along the top along with averages in minutes, hours and minutes (h:m). Also listed are n numbers for each event, stage duration (in minutes and in h:m) and standard deviation (STDEV) for each event. % of developmental time is show for each stage (%TED). Raw data for time-lapses 1-4 are shown in columns L-O along with details of embryo orientation, optics and time intervals used. Columns Q-T show the same time-lapses after a time adjustment has been made. In brief, 10 minutes is added for each unrecorded cleavage cycle (i.e time-lapse 4 starts at 11min in the raw data, therefore the start of the movie is C3 + 9min. By adding 9 min we arrive at the start of C3, by adding another 10 min we arrive at the start of C2, and adding another 10min the start of C1. Hence, to normalise this movie I add 9+10+10= 29min). Alternating white and grey rows mark events occurring within a stage. Stages marked in blue indicate heterochronic shifts in developmental events.