Evolutionary conservation of lampbrush-like loops in drosophilids

Table 1 Analysis of various aspects of male spermatogenesis in different drosophilids

species (in alphabetical order)	sperm length (mm)	sperm tail entering eggs (mm)	T53-F1 staining in tails	loop size	Loop shape	overlap	nucleus shape
D. acanthoptera	5.83 ± 0.09	(++)	yes	3	d	weak	S
D. americana	5.22 ± 0.02	nd	yes	1	d	weak	S
D. bifurca	58.29 ± 0.67	1.6	yes	1	d	strong	O
D. funebris	8.29	nd	yes	1	d	strong	S
D. hydei	23.32 ± 0.51	1.31	yes	2	d	strong	O
D. littoralis	7.72 ± 0.08	(++)	yes	3	f	strong	S
D. mauritiana	1.036	nd	yes	2	f	weak	S
D. melanogaster	1.9 ± 0.01	1.78	yes	3	f	strong	S
D. mercatorum	nd	nd	yes	3	d	strong	O
D. novamexicana	6.72 ± 0.15	nd	yes	3	f	weak	S
D. pseudoobscura	0.36	0.36	yes	2	d	strong	S
D. sechellia	1.649	nd	yes	2	d	weak	S
D. simulans	1.14 ± 0.01	1.14	yes	3	d	weak	S
D. tessieri	1.0 to 2.0	nd	yes	3	d	none	S
D. texana	5.08 ± 0.04	nd	yes	2	d	weak	S
D. virilis	5.70 ± 0.16	nd	yes	3	f	weak	S
D. yakuba	1.681	nd	yes	3	f	none	S

Data reported in the first three columns are partially taken from [13, 41, 49-51], and (++) indicates that almost the entire sperm tail enters the egg. Columns 5, 6 and 7 refer to the structures decorated by T53-F1 inside primary spermatocytes, as described in the Results section. In particular, loop size refers to the relative extension of the immunostaining inside the primary spermatocyte nucleus, 3 meaning very extensive loop, and 1 meaning very small loop. Loop shape indicates its filamentous (f) or dense (d) appearance. Overlap is "strong" when immunostaining and phase-contrast visible structures inside primary spermatocytes nuclei are the same, "weak" when the structures are only partially overlapped; "none" indicates that immunostained structures do not have a counterpart visible by phase-contrast. Nucleus shape, S indicates spherical or nearly spherical, O indicates other shapes (see Figure 2 and the Discussion section for further explanations). Cytological data about D. melanogaster, D. hydei, D. virilis and D. novamexicana partially come from [30].

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