Accessory gland size changes during recovery
We here tested how developmental temperature affected accessory gland
(AG) growth in young males. As developmental temperature affected male
body size (GLM with a gamma error distribution: Deviance = 1.075,df = 4, F = 228.33, P < 0.0001) and this
scales with organ size, we corrected for body size in further analyses
using wing length as a proxy. Overall, males were smaller on day 6 after
eclosion when they developed at higher temperatures (29: 1.25mm ± 0.007;
29R: 1.23mm ± 0.007; 31: 1.21m ± 0.011; 31R: 1.17mm ± 0.009) than
control males (1.37mm ± 0.007, see Supplementary table S4).
We observed a clear reduction in AG growth during the first six days
after eclosion in males exposed to elevated developmental temperatures
(Fig. 4A, table 2). The reduction in growth was gradual: the higher the
temperature, the slower the increase in AG size, resulting in
significant differences on day 6. Surprisingly, the growth trajectories
did not differ for males raised at 29°C and kept at the growth
temperature and those allowed to recover (see post-hoc test in
Supplementary table S5). Interestingly, AG sizes of recently eclosed
males (day one) were fairly similar. In a second analysis we only
compared AG size of treated males and hence, excluding the control group
from the analysis, using larval temperature and the possibility of
recovery or not as fixed variables. This revealed that the 31°C recovery
treatment resulted in males having significantly smaller AGs compared to
males not allowed to recover (GLM with a gamma error distribution,
recovery: F = 18.88, df = 1, P < 0.0001).
By day six, the reduction in size was 12.8% for males of both
treatments exposed to 29°C and 40.3% for those exposed to 31°C compared
with the control group.
We next assessed whether the allometric relationship between the gland
and body size is also altered. The regression analysis between both
factors (see Supplementary table S6 and Fig. S3) indicates that in the
two elevated treatments a hypometrical relationship prevails
(b<1) highlighting that the gland is smaller than expected for
the body size, while it tends to be isometrical in males grown at 25°C
(b=1). Thus, differences in AG size can be attributed to altered growth
patterns due to temperature. Overall, these results suggest that AG
maturation is inhibited by elevated temperatures with males ultimately
having smaller glands.