Fig 1.
False cloaca and female dummy used for experimental ejaculate collection in male house sparrows.
(a) Example of a false cloaca prototype, which was filled at the larger opening with 4μl PBS before being inserted up until the wire into the female dummy. Rear (b), and side (c, d) view of the single female dummy used in sperm collection trials. Pictures courtesy of: Elena Beirer.
Fig 2.
Massage technique used for male house sparrows.
(a) A male was positioned on his back and his cloacal protuberance exposed. (b) Pressure was gently applied at the base of the cloacal protuberance using three fingers. (c) Experimental ejaculates were collected using a ring-marked capillary. Pictures a) and b) courtesy of Elena Beirer and c) Julia Schroeder.
Fig 3.
Schematic overview of experimental protocol.
Whereas the time and sequence of massage and faecal sampling was randomised, female dummy trials always took place before the faecal and massage sampling.
Fig 4.
Length measurements of house sparrow sperm.
Example of measurements of single sperm components: head: nucleus (red) and acrosome (pink), midpiece (green), and flagellum: tail (cyan) and midpiece (green). Total length was calculated by using the sum of flagellum and head length. Note that whereas the transition from midpiece to head and the end of the acrosome are visible in light microscopy; the acrosome and nucleus cannot be precisely differentiated and are portrayed here only to demonstrate the composite nature of the head measurement.
Table 1.
Descriptive summary statistics of length measurements of house sparrow sperm.
Table 2.
(a) Observer repeatability, and (b) individual male repeatability for house sparrow sperm length measurements.
Fig 5.
Sperm length (μm) differences in relation to sperm sampling method in house sparrows controlling for relative order of massage to faecal sampling.
Sperm heads (a), and midpieces (b) were significantly shorter sampled from faeces [17] (823 sperm from 41 males) compared to abdominal massage samples [19,20] (822 sperm from 45 males). Filled dots represent means and vertical lines represent 95% Bayesian Credible Intervals (CrI).
Fig 6.
Individual males' sperm length (μm) differences in relation to sperm sampling method in house sparrows.
We present individual raw data of males (n = 16 males) for which we had a total of two faecal and two massage samples. Thin grey lines connect the measurements for massage and faecal samples of individual males per trial. Pink lines connect the average measurements of massage and faecal sampled sperm across trials.
Table 3.
Length (μm) of house sparrow sperm in relation to sperm sampling method controlling for relative order of faecal [17] to massage samples [19,20].