Family Life on a String for a sandhopper

A monogamous sandhopper makes it happen

If someone spends years and years researching for his doctorate degree and devotes a considerable time of his life to the study of a half-centimetre long multilegged, marine critter, you would expect this creature to have some irresistibly attractive features, right? So, I was very excited when Dr Helmut Stephan of Kiel University showed me “his” Dulichia porrecta, an amphipod (and therefore a ‘relative’ of sandhoppers) living at depths of 40-60 m or deeper in sub-Arctic oceanic waters including some patches of the Baltic Sea. Keeping this animal in captivity in the lab requires patience, water in the aquarium cooled down to a constant 12°C, and lots of cultures of the right algal plankton mix as food for these crustaceans.

But it’s all worth it, for the behaviour of this sandhopper-relative, belonging to the crustacean order of the Amphipoda, is so incredible, so unbelievable fascinating that you’d forget about your favourite TV-programme (at least I did). Male and female Dulichia live in a monogamous relationship. Although both have spin glands on their feet, it is usually the female that “knits” a vertical, about 2 mm thick stocking, some 10-15 cm long, and fills it with detritus and very small sand grains. Male and female then ascend this construction, which stands anchored on the seabed, and will spend the rest of their lives on this string.

The two adult animals moult, mate, and have 20-40 babies, which are released from their mother’s pouch (a characteristic feature of all amphipods) one by one and deposited carefully on the supportive family stalk. The baby “Dulichias”, too, spend their childhood and youth on the string, combing the water for planktonic algae, their principal food, until they get too unruly and big and are then plucked off by their parents and seemingly “thrown away” into the currents to fend for themselves from then on.

One brood reared to maturity, others may follow. Occasionally unexpected visitors, whose own stalks have collapsed or got destroyed, perhaps by a fish, may arrive. Should such a new arrival be a female, then the male would “play the gentlemen” and be willing to let her stay, but the female stalk-builder would be furious and fight the newcomer off in rather an “unfeminine” way. If the unexpected guest is a male, however, a fight between the two males is the rule, with the female stalk-owner being a passive onlooker.

The construction of the stalk, the birth of the young, the feeding process, the fights and the sheer fact that we are here dealing with a monogamous, semi-social crustacean are enough to make the heart of a zoologist beat faster. I simply had to get hold of some of these animals to study them and decided to examine their eye structure by transmission and scanning electron microscopy, which turned out to be an interesting publication as the eye surfaces of the Dulichia porrecta adults were covered by a dense pelt of tiny cuticular hairs. Thank you, Dr Stephan, for having enriched the world with your discovery of the wondrous family life of Dulichia porrecta (and my list of publications with another interesting paper)!

© Dr V.B. Meyer-Rochow and, 2018.
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