Submitted by [deleted] t3_yu3hs6 in askscience
K-Strategy, the process in which a species when breeding focuses on only a few offspring is common amongst birds, mammals and other vertebrates. But is there any case of it among insects or are they all r-strategists? If they are, what is the "simplest" animal with the K-Strategy?
Evolutionarily, investing the time and resources while the offspring are gestating, after birth, or before fertilization is probably as good as the same thing. At least as far as K-strategy etc terminology is concerned, right? One new tarantula hawk per tarantula is a strategy based on it working most of the time, vs sea turtle hatchling death gauntlets for a vertebrate opposite example.
I saw a vid of sea horses where it stated only 1-2% of around 1000 or so births per father survive to adulthood. Brutal odds.
You can actually do this math for any species at all, without knowing anything about its biology except how many offspring they tend to have.
Think of it this way: animal and plant populations may fluctuate wildly from year to year, but in the medium-term, we can assume that the per-year average total population of a species is more or less stable — neither increasing or decreasing. This necessarily means that (assuming equal sex ratios, which most species have) each female is having, on average, two offspring per year that survive long enough to have their own offspring. That's one offspring per female to replace herself, and one to replace her male partner. Some females will have much more than two offspring survive to adulthood, and some will have none, but the per-female average is approximately two.
So if you find out that a species tends to have approximately 1000 offspring, you can divide 2 by 1000 to get the survival rate. If the typical litter size is four, you know that only half of them on average will make it. If a species tends to have a million offspring, it's two in a million.
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Does that mean that social insects are k-strategist? Think about it. For one queen bee to beget the next queen bee, she produces an entire colony of workers and drones, which in turn put in an enormous amount of work to build and maintain a hive. That’s a lot of work just for the genes to be passed down to the next colony.
I think its better to think of the colony as a single reproductive evolutionary unit, not as a collection of individuals. Ant colonies produce a large number of new queen's and drones for nuptial flights. Unless they are very lucky to find a good unoccupied spot most of the next generation perish.
In that sense ants don't put too much investment into reproduction.
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Maybe. They probably have fairly low infant mortality, since the babies are all being fed/cared for until they are mostly grown up.
I find it interesting that the Pepsis wasps link their success with that of tarantulas. It seems counterintuitive to need tarantulas in order to breed, but each offspring kills a tarantula. Do they have the ability to change host incubators if tarantulas were to become unavailable?
This is true of any specialist predator though. Basically it just can’t be TOO successful or it wipes out it’s host/prey opportunities
It's often true of more generalist predators as well, even though they are dealing with a broader spectrum of prey species. Population booms and crashes are quite normal over any reasonable timeline.
Well, it's self correcting. If there are plenty of tarantulas, they have plenty of opportunities to make babies. If they hunt them to scarcity, there won't be as many babies and tarantuals will again flourish. Seems pretty clear they have an equilibrium going. At least until humans destroy the habitat of either.
Isn't this the same as any parasite species for example?
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Not always. It depends on the mode of infection. If a parent hunts down a host for direct infection, they don't need many offspring. For other parasites, especially those that don't have a free-living adult form, they often produce huge amounts of eggs or larva. Think of parasitic worms, for example. Most of the young never find a host, so they need numbers.
Evolution doesn't plan through logic, just what works. And it certainly doesn't account for the interruption humans have imposed on the natural order of things (except for some modern responses we're beginning to see from anthropogenic pressures).
I agree, I understand how natural succession works…and clearly it works in this case. I just find it interesting to see one species place its entire future on one other species…kind of an all the eggs in one basket approach. I suppose if tarantulas were to disappear, the wasps would also go extinct, unless some had the ability to adapt and use another host. Is there cases where we see these wasps successfully, albeit rarely, use another host for their eggs?
You're anthropomorphizing the very concept of 'a species'. There is no 'species of these wasps' entity that specifically places it's future onto any thing... it's just a load of individual wasps bumbling about doing whatever and just so happening to have genetically condensed on doing something that kind of works well enough.
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There are many therophosids wich are not tarantulas but are commonly misidentified as such. (Trapdoors, mose spiders, and funnel webs are examples) the ecologocal difference as might pertain to darwinistic theory is geographic distribution, their relative speed, the strength of their venom, and the nature of their exoskeleton.
Thanks u/penis_in_my_hand!
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Do you at least have Diet Coke Wasps?
How long between the egg laying and hatching? Is the tarantula paralysed the whole time until hatching, or does it wear off and it goes about its life for a while with a ticking bomb inside it?
I hate when somebody asks a question that I didn’t even realize I wanted to know and there hasn’t been an answer yet… now I’m going down the rabbit hole.
Accordingto this article the tarantula is gravely wounded and the wasp eats the blood and innards that come out of the wound before burying it alive. The paralysis eventually wears off before the larvae hatches and eats it, but doesn’t recover enough to escape the buried tomb before being eaten alive.
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These terms are inherently relative rather than describing any definitive thresholds, but among insects hunting wasps and solitary bees are perhaps the most "K-selected". These species provide significant parental care to offspring in the form of food provisions (pollen/nectar in bees, and usually other paralyzed arthropods in wasps) and as a result have relatively low reproductive output on a per-individual basis.
For example, Punzo 1994 studied the tarantula hawk Pepsis thisbe, for which he estimated an average lifetime fecundity of 13.4 eggs/female. As you can imagine, the process of hunting down and paralyzing a tarantula, digging a nest, laying an egg, and burying it takes many hours. Also in line with the general traits of "K-selected" species, these offspring have fairly high survival rates with about 65% estimated to reach adulthood.
Another study by Bosch and Vicens 2006 of the mason bee Osmia cornuta over several years reported an average of about 10 eggs laid per female, and similarly low mortality rates. Unlike tarantula hawks this species does at least lay multiple eggs in one nest, but must make many trips to collect pollen, nectar, and building materials, taking about two days per offspring on average.
In contrast, a more "r-selected" species like a monarch butterfly may lay many hundreds of eggs in her life, but mortality rates are typically above 90% (Zalucki and Kitchling 1982).
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The first offspring of a new ant queen are called nanitics and are special. They exhibit a lack of curiosity, and display more defensive characteristics, in an effort to balance the risk/reward of exploration for an early colony. If a nantic dies then 50%+ of the workforce dies which would be a dire scenario, but later one death is a drop in the bucket so exploration is prioritized.
It's not exactly what you were asking, but there is some variance in breeding strategies :)
EDIT: fixed typo, nantics -> nanitics
Fascinating! It took me a second to look up, turns out they are called nanitics -- commenting not to grammar police you, but in case anyone else was curious to find out more too.
Hi, a tsetse fly, has a kind of pregnancy. The female sucks mammalian blood, a high energy source. She carries only one offspring at the time, the larvae is in a kind of uterus and is fed a secreted substance. The larvae is 'born' as a third instar. And very quickly enters a pupea stage. So compared to other flies this particular species, could be called a K strategist I think.
Severel insects are k-strategist. It is however important to understand k strategy exhibited by insects is different from avian or mammalian examples. Mainly because of the limited developmental needs of the offsprings (little to no learning, no sociality, etc.) and also due to the rapid development of insects. Most of the time the insect kstrategy aims to shorten the development, not lenghten it.
It can be found among hymenopterans. Some example have been pointed out by others. One could also include eusocial hymenopterans multiplicating through colony-fission such has several army ants species or bees as a kind of k-strategist.
Some beetles, like several Passalidae, a few Scarabeidae and some Silphidae exhibit advanced parental care. The most extreme known instance is Cylindrocaulus patalis. The female lays 1 egg per reproductive cycle (1 per year) and exhibit biparental care (predigesting food, grooming, feeding trophic eggs) for the offspring all the way to adult stage. The adult offspring then hibernate with its parent.
Copris sp., and especially C. hispanicus, a true dung beetle, will lay between 4 to 6 eggs in as many dung brood balls ressembling clay pots. It is believes the female stays on the brood chamber until the brood ball is mostly consummed by the larva. The female will right the broodball, maintain the chamber and exit tunnel, and defend it from intruding insects.
Some Nicrophorus species (also called burrying beetles) also have a similar strategy, but more eggs are layed on the carcass.
Various species of scorpions maybe?
While not an insect but an arachnid, quite a few Amblypygi species fit the bill.
Primarily in the genus Charinidae - because they are small and slow growing, their broods are small among the group and their babies are relatively large. The mother stays with the brood for a number of weeks.
They also display parental care and limited eusociality.
Interesting. Do you have any papers to suggest so I can read further?
Yes! I'll look this evening. Charinidae aren't studied very much, but most if not all Amblypygi exhibit the same traits except smaller broods.
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K strategy seems counterproductive to an insects main strengths. Small resource investment. Short life/death cycle for high evolutionary adaptations. (With these two things in mind, getting vast numbers created greatly amplifies your adaptive ability, like a virus)
And it would be a drawback when you consider their weaknesses. Given their size they have little ability to control their temperatures, pressures, and other things. So their ability to keep “homeostasis” is very negligible, which is their main downfall. Heavily investing in one area or one offspring and NOT spreading as rapidly as possible is inherently counterproductive to their survival chance.
As an analogy, I’ll equate it to us. Imagine how much our survival chances would increase if we got off this planet and had other planets that also could spread life? Focusing on just this one is a death sentence, as every couple 1,000,000 years, life ending threats happen.
But keep in mind that having a ton of offspring is useless if none of them make it to adulthood.
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penis_in_my_hand t1_iw7l8h2 wrote
Pepsis wasps (tarantula hawk) will fight a single tarantula, paralyze it, drag it back into the spider's burrow, and lay a single egg it. Then when the egg hatches the baby wasp eats the tarantula alive, going for the least vital organs first.
The parent puts considerable effort into a single offspring.
But the momma wasp doesn't hang around and care for the baby. It's more of the entomological equivalent of a trust fund...