The Godmother Nightshark

Swordsharks, a clade of unusually intelligent and frequently social descendants of swordtail fishes, remain a highly successful predator guild in the middle Cryocene, 65 million years PE. These fishes are uniquely coordinated hunters and communicate with one another via visual cues in body language and boldly flashing markings. Groups divide up smaller bait fish into tightly crowded balls, then split and divide them amongst themselves. Swordsharks are also placental, nourishing embryos in utero via a tie to their own bloodstream and so producing only a few young at a time but giving birth to offspring which are very large and well-developed and have a high chance of survival.

In the middle Cryocene, one of the most quintessential examples to be found of these social predators is the godmother nightshark, a remarkable animal (with a rather strange name, that nonetheless sums up its behavior quite well).

The godmother nightshark is a nocturnal predator, relying on acute vision to catch smaller fish under cover of darkness, which shows highly pronounced behavioral sexual dimorphism. The male is a lighty-built, open-water pursuit predator, while the female is larger, moves more slowly, and forages along coastal habitats near the sea floor, catching prey as it sleeps. The female of this species shows some of the most well-developed pro-social behavior of any fish ever to live, and forms life-long relationships with related females. Clans of two to as many as twenty such females are formed based on kinship, most often siblings, mothers, aunts and cousins. These groups live together and cooperatively hunt for prey. Movements of the tail sword are utilized to communicate intention and emotion, angling in different ways as a sort of meter of the owner's emotional state as well as to indicate what they will do next in the hunt. Males lack any sort of sword at all as it would interfere with their higher-speed lifestyle, and thus their cooperative hunting behavior is more opportunistic, self-centered, and less cohesive. Females coordinate to drive smaller fishes from hiding places and into anothers' waiting jaws. Their sharing is not only a matter of one sometimes getting the fish, then another taking a turn, but rather frequently involves highly ritualized parting-out behavior where the individual which successfully obtains a prey item at the expense of another will be solicited by the other less-successful clan members to share. Those who have had less hunting success will sidle alongside her and vibrate their jaws against her throat, which in turn results in her regurgitating a portion of the prey for the other member(s). This ensures every member of the hunting party is always fed, and in turn is strong enough to hunt again the next night. This food-sharing is done reciprocally, strengthening social bonds and trust between individuals in the clan.

Cooperation hunting is common to swordsharks. Food sharing is much less so, but even more rare is the degree of parental care provided by the godmother, which not only cares for its own offspring but those of other females in their clans. Two offspring are usually birthed at a time, and all of the individuals in a group take turns guarding the birthing mother and then the newborns from predators during this highly vulnerable time. The newborns stick close to any nearby adult and over a few hours imprint upon the scent of its clan. Though well-developed and able to hunt small prey for themselves almost from birth, the young are primarily fed by all of the adults via regurgitation of finely chewed particles for the first eight weeks of their lives. Females may spend a lifetime with their clan, though groups will break apart when they grow too numerous for local food resources. Males go off on their own around one year of age and join into bachelor groups of largely unrelated males, but may occasionally return to their natal groups for several months later, only being aggressively excluded once they are sexually mature. This occurs for very good reason - adult male godmother nightsharks are both cannibalistic of the young, and extremely aggressive in pursuit of mates.

above: a godmother nightshark gives birth, guarded from attack during her most vulnerable moment by a roving male by another female clan-mate.

Indeed, it is this latter attribute which is the primary cause for the evolution of their species into such disparate male and female morphs. To better dominate mates is also why the male has remained social, despite being a relatively poor cooperator with limited capacity for body language communication due to the lack of a tail sword. They need groups to overpower the larger females to mate with them. This is a species engaged in an evolutionary arms race between the sexes, where males have become increasingly aggressive in seeking to breed, while females have evolved their own counter-measures to avoid undesired breeding and so choose their own partners. To avoid such aggressive males, which seek to violently force copulation, females adapted to band together and so collectively drive off male pursuers that might injure them in their drive to reproduce. This arms race has begun selecting for two very distinctly behaving morphs of males which seek to overcome this barrier to reproduction either through increasing aggression further, or conversely, by being gentle and romantic. Females prefer romantic males, which are a distinct, uncommon morph with much less testosterone, which shows more normally female-specific behaviors including pro-social food-sharing. Romantic morph males must put in a lot of effort to successfully breed and are less likely to succeed than their belligerent relatives, which means they are always less numerous. They play a long game to win the favors of the females, and will frequently leave their bachelor groups and trail behind female clans for days at a time, bringing small gifts of food before being accepted to mate.

Aggressive males, in contrast, don’t wait to be invited. Entire packs descend upon female clans and seek to isolate one at a time and forcibly copulate. If they are able they will kill all of the young first, which reduces the defensive response of the females and makes them less reluctant. It is thus in the benefit of the female to live in clans as large as possible to defend themselves from these bands of rapist males and have the opportunity instead to cavort with gentler options, yet ultimately this is dependent on available food resources. Where not enough prey exists for large clans to form, females must contend with aggressive partners. For the survival of the species this is not all bad - such aggressive males are likely to produce initially stronger young at birth, which have better responses to avoid predators. Yet this selective pressure, if unchecked over generations, can produce males so aggressive they are likely to kill females entirely before breeding. The population could not survive with only aggressive males becoming increasingly violent over the generations. The relatively rare but highly sought after romantic males maintain a balance in the population as a whole, and persist despite being less individually successful because their genes limit the aggressive tendencies of the population as a whole.