So here’s a stupid question

Obviously, geographical separation is what – OK one of the things – that leads to speciation. The oceans are a lot less geographically separated than the land masses. So, we get rather wider distribution of sea species than we do land ones.

Sorta, at least.

I can imagine that a barrier in the sea is the Equator. Not so much currents and stuff but heat. Down deep even that doesn’t matter of course. But I could imagine at least that we get N Hemisphere fishies and S Hemisphere ones.

At which point, how true is this?

Take, say, cod. I know there’s a Pacific cod as well as an Atlantic one. And they’re both up in northern waters as they don’t like it hot. But, and here’s the thing, do we have closely related species which are S hemisphere? Or other, cognate species? Or something entirely different occupying the niche? Or does the niche not exist?

No particular reason, just a question that crossed the synapses.

19 comments on “So here’s a stupid question

  1. A barrier is also that large tracts of the oceans are deserts and do not support much life.
    The northern and southernmost latitudes support krill and similar organisms in greater abundance, hence why one is more likely to encounter large shoals of bigger fish and whales and things.

  2. A Tale of Three Tails: Cryptic Speciation in a Globally Distributed Marine Fish of the Genus Seriola

    https://www.asihcopeiaonline.org/doi/abs/10.1643/CI-124-224
    Genetic data are increasingly being applied to re-evaluate past taxonomic hypotheses and better understand the evolutionary patterns and connectivity among regional populations of cosmopolitan species. This is of particular importance for heavily exploited, commercially important species. The phylogenetic structure of the Yellowtail Jack, Seriola lalandi Valenciennes, 1833, was investigated using genetic data from 42 individuals collected from California, the Pacific coast of Baja California (Mexico), the Gulf of California (Mexico), New Zealand, Japan, South Africa, and Chile. An analysis using S. dumerili as an outgroup and combining the sequences of two mitochondrial genes (CR and COI) and four nuclear genes (RAG2, EHHADH, UBE3A, MLL) was used to determine the level of genetic divergence among samples from different geographic regions. Bayesian and Maximum Likelihood analyses utilizing combined mitochondrial gene (mtDNA) or nuclear gene (nucDNA) data supported the existence of multiple regionally restricted clades with mtDNA analysis identifying four major clades and nucDNA supporting three. Both mtDNA and nucDNA trees were very similar in topology, which was reflected in the combined total evidence phylogram. These clades were highly supported with Bayesian posterior and bootstrap probabilities ranging from 90 to 100 percent for the three major clades that were recovered in both mtDNA and nucDNA trees. These clades represent regionally specific specimens collected from the 1) Northeast Pacific, 2) Northwest Pacific, and 3) Southern Hemisphere. Morphometric analysis (MDS and ANOSIM) of available meristic data on the number of soft dorsal-fin rays, anal-fin rays, and total number of gill rakers separated specimens among the three regions identified by genetic analysis (P  =  0.05). Based on the phylogenetic structure within this taxonomic unit as evidenced by genetic data and significant meristic differences among these regional lineages, we conclude that three cryptic species currently bear the name Seriola lalandi Valenciennes, 1833. We propose the resurrection of two currently available names based on nomenclatural priority. The Northwest Pacific species name should revert to Seriola aureovittata Temminck and Schlegel (1845) (type locality Japan), and the Northeast Pacific species to Seriola dorsalis Gill (1863) (type locality Cabo San Lucas, Mexico). Seriola lalandi Valenciennes, 1833 (type locality Brazil) should apply only to the species in the Southern Hemisphere.

  3. Those numbers are types, not dates,I assume.
    I’m sure that they didn’t know about DNA in 1833.

  4. You are talking about cod, a Northern Hemisphere delicacy. Sadly you never mentioned Deepwater Hake, fished off the Cape of Good Hope in the cold Antarctic waters. If ever you get to Southern Africa and see hake on the menu, try it. I think it beats cod and occasionally buys it from the Tescos fishmongers whenever I am homesick.

  5. I’ve read that the N Atlantic lobsters from Canada/USA are less tasty that the North Atlantic lobsters on our side. I don’t eat lobster often enough to have view of my own.

    Trees are an interesting one: many of the broadleaf trees in New England are pretty similar to the trees of Old England but just different enough that the American ones are far easier to clear e.g. the tree will die of you ringbark it or chop down the trunk, rather than throwing up new stems and soldiering on. Or so I’ve read.

    They are also more combustible though whether that’s a varietal difference, or just a reflection of drier, hotter summers, I don’t know.

  6. You people have a lot of time on your hands.

    Not that it’s not interesting. But those of my fascinations indulged in idle moments are far more so. Like, um …

  7. Since moving o New Zealand from the UK I have been struck by how similar a lot of the birds are to the UK ones . For example, although smaller, the heron here is the same shape and flies in the same way,The Kingfisher is also similar in size and shape.
    Presumably they have evolved in the same direction because they hunt similar prey .

  8. Dearie,

    The only redeeming feature of the US cuisine is the abundant seafood. And the size of it compared to Europe.

    I don’t like lobster much. You work on it for an hour, are left with bloody hands, and get enough meat for half a sandwich.

    In the 17th century it was made illegal in Massachusetts to serve it to prisoners more than a certain number of times a week, it being deemed cruel to expect them to eat it too often.

  9. Abundant seafood at Cape Cod, certainly. But when I first went there many Americans pretty much refused to eat seafood (other than shrimp and prawns, perhaps). It struck me as odd because their beef was pretty poor, being unhung, and virtually none of them ate lamb. And yet they avoided seafood. Rum coves.

    By contrast, I get the impression that more recently they’ve become big consumers of tuna. Is my impression correct?

  10. @dearieme
    All the steak I’ve eaten in the US, from chain eateries to smart Manhattan restaurants, has been at least “28-day dry-aged USDA Prime”. Keens – a couple of blocks from Penn Station/Madison Square Gardens and the Empire State Building – do an excellent Mutton Chop (I think I’d describe it as lamb), but I agree that’s not something you normally find on a US menu.

  11. So they’ve decided to hang their beef – now there’s an advance since my day. (Back then the usual ad said “100% US government inspected beef”.)

    When we lived in Queensland we were most amused that many people were puzzled that one restaurant chain served beef that was better than everyone else’s. To our palates it was obviously because they hung the beef. Enquiry revealed that we were right. So there you have it: into the early nineties hanging beef was still pretty unusual in Oz.

  12. So was the tropical fruit but the apples were rubbish. They made a big effort to keep out the superior NZ apples. So much for a free trade agreement, eh?

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