Reproductive traits of Macrobiotus hufelandi during a long-term field study with notes on Paramacrobiotus richtersi and Diphascon pingue (Eutardigrada)

We studied reproductive traits in populations of the eutardigrade species Macrobiotus hufelandi, Paramacrobiotus richtersi, and Diphascon pingue from a carpet of the moss Rhytidiadelphus squarrosus in the Black forest, Germany, over a period of 53 months. Specimens were fortnightly extracted, measured, and divided into dead and living individuals. The living specimens were divided into juveniles, ovigerous females (i.e. females with mature eggs and immature, but vitellogenetic eggs), and females with undifferentiated oocytes. Males were never found during the investigation period. For the most abundant species, M. hufelandi, it was shown that i) ovigerous females were found throughout the year; ii) reproductive activity (expressed as the percentage of ovigerous females in the total population) was highest from January to June, but peaks in these months varied considerably within the investigation period; iii) development of eggs may be considerably delayed compared with data obtained from cultures; iv) presence of ovigerous adults and juveniles was nearly opposite, i.e. the more adults the fewer juveniles were found, and a maximum of adults was followed by a maximum of juveniles with some delay and vice versa; v) number of oocytes, as well as length and percentage of ovigerous females relative to the total number of specimens appeared to be negatively correlated, whereas percentages of juveniles (<260 μm in length) appeared to be positively correlated with temperature. Other correlations included humidity (number of oocytes, negative; percentage of juveniles, positive) and the sum of hours of sunshine (length and percentage of ovigerous females, negative; percentage of juveniles, positive). The relatively low numbers of P. richtersi and D. pingue collected during the investigation period did not allow a more detailed analysis, but here as well ovigerous females were found throughout the year.