To my knowledge, when foot webbing bird phylogeny has been reconstructed
it's always been connected to mutations in Gremlin1
https://www.nature.com/articles/s41598-020-64786-8
It seems this individual could just be a mutant that lacks a functional
copy of the gene.



Longer: in ontogeny (development) programmed cell death is as important as
proliferation. One of the great beauties of development: reach your arms
out in front of you and put your hands together, matching finger to finger,
between left and right hands. They match with near perfect accuracy!,
despite the fact that the last time these cells directly communicated was
when you were a mere several thousand cells (or less). The genetic programs
that separated your arms from your body and in turn converted clubbed
endings into paddles and paddles into digits were programs that marked
certain cells for death (apoptosis), much like Michelangelo's "The
sculpture is already complete within the marble block, before I start my
work. It is already there, I just have to chisel away the superfluous
material."

Bone morphogenetic proteins (BMPs) control this is your hand and a birds
foot, resulting in programmed cell death of the tissue between your fingers
while you're in development. In their evolution, some branches of birds
gained webbed feet by gaining a gene to inhibit these BMPs, then some
species still lost the webbing again in cases of convergent evolution. I
would guess this gull is an exceptional individual, with (lacking the
knowledge of a better candidate) has a non-functioning copy of the gene (or
for some other reason expression was suppressed) that normally prevents
this species/genus/order/family of birds from gaining independent digits.
If it's truly a pioneering individual that breeds successfully, who knows…
maybe we'll one day see a more successful species of land or arboreal
perching-gulls… the stuff evolution acts on.

Stephen J


On Wed, Feb 23, 2022 at 12:30 PM Dennis Paulson <dennispaulson at comcast.net>
wrote:


> Has anyone heard of anything like this? I haven't.

>

> Dennis Paulson

> Seattle

>

> Begin forwarded message:

>

> *From: *Alexandra MacKenzie <mizmak at gmail.com>

> *Subject: **Gull without webbing*

> *Date: *February 23, 2022 at 12:10:40 PM PST

> *To: *dennispaulson <dennispaulson at comcast.net>

>

> Hello Dennis,

>

> I retired to Richland in 2018, where there's been a Slaty-backed Gull

> wintering over for the past few years. Today I ran into one of the birders

> (Elke Davis) who has taken tons of photos of it, and she was curious about

> an anomaly -- it has no webbing on either foot. Genetic abnormality? I

> said that I'd ask the expert if he had ever run across such a thing, so

> here I am, asking you! There is a great pic on Elke's ebird of one of the

> feet:

>

> https://ebird.org/checklist/S96132278

>

> She says both feet look the same. Wonder if it would have trouble

> swimming? It seems to be surviving just fine!

>

> Any info would be greatly appreciated.

> I always enjoy seeing your FB posts.

>

> Best wishes,

> Alex MacKenzie

>

>

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