RSS Diversity and forms of the Pseudanthias ventralis species flock: How many are there?

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  1. MASA Admin

    MASA Admin Moderator

    8 May 2007
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    In light of our recent trend in picking apart cryptic species within a given complex like we did for Pseudanthias pascalus and Nemateleotris helfrichi, we continue yet again with a rather massive undertaking. This time with Pseudanthias ventralis. This beautiful species is wide ranging across much of Oceania, but seems prone to insular variations with at least three major and rather distinct representations that can be grouped based on coloration as well as geographical range. The fluidity of its forms suggests its susceptibility to speciation, with one isolated populace in Hawaii already awarded full taxonomic upgrade. It is Pseudanthias hawaiiensis.

    It is of course important to note that this article is not in anyway a scientific standard for splitting a species, but rather a suggestive piece based on comparison and analysis of various forms within the complex. In the range map above for P. ventralis you can see that it has been roughly divided into a cross section of four, with major distinctive groups being found in four quadrants. These are the Southern Pacific and French Polynesian island chains, the Australian region encompassing New Caledonia and the Coral Sea, the Marshall Islands and Japan with Mariana as an intermediate, and finally Hawaii; where speciation has already awarded the area with the endemic P. hawaiiensis.

    Cook Islands, Southern Pacific, French Polynesia and the Pitcairn Islands

    [​IMG]Pseudanthias ventralis in its Southern Pacific and French Polynesian range.

    The type locality of Pseudanthias ventralis is Gannet Ridge, off the Pitcairn Islands. For that reason, the forms here and the surrounding locales should by right depict the actual representation of the species. We’ll explore these, as well as the other forms in a clockwise manner based on the quadrants of the map above and try to pick out any phenotypic or morphological differences amongst the various forms.

    [​IMG]Southern Pacific and French Polynesian forms of Pseudanthias ventralis. A1 – P. ventralis (Male, Cook Islands). A2 – P. ventralis (Female, Cook Islands). B1- P. ventralis (Male, French Polynesia). B2 – P. ventralis (Female, French Polynesia). C – P. ventralis (Male, Pitcairn). D – P. ventralis (Male and Female, Southern Pacific). Photo credits A1,A2 – LemonTYK. B1,B2,C – John Randall. D – unknown.

    The collage above depicts various specimens from the first quadrant of the Southern Pacific and French Polynesian range. In this it also includes the Cook Islands and the Pitcairn island groups. Seeing as the type locality for the species originates from here, these should be considered the benchmark type and all other regional forms following should be compared carefully with these.

    [​IMG]Male Pseudanthias ventralis with characteristics highlighted and arrowed in white. Photo by LemonTYK.

    In P. ventralis, the males are steely purple overall with the head encapsulated in yellow. The dorsum just beneath the dorsal fin is yellow washed, but is peppered so heavily in purple spots that in some extreme cases, the underlying yellow is obliterated completely. These purple spots tend to remain circular and distinct, which is an important characteristic when comparing with specimens in other locales. The dorsal fin is red only on the anterior spiny portion (clear in dead, preserved specimens), and hyaline or yellow tinted on the soft portion. The leading edge of the soft dorsal fin is also unmarked with no purple lines. Caudal fin is largely clear and unmarked, except for a pair of vertical purple lines. The anal fin is clear, but has a strong purple line delimiting a more deeply colored region corresponding to the anal spines and first rays which form the elongate leading edge of the fin.

    The females share the same steely purple ground coloration, but are unmarked except for a yellow dorsal fin which creeps to a sliver of the dorsum before ending obliquely at the caudal peduncle. A red arching stripe separates the two colours near the posterior portion of the dorsum. Females lack secondary coloration such as the purple spotting that the males possess.

    Coral Sea, Vanuatu and New Caledonia

    [​IMG]Pseudanthias ventralis in the Coral Sea and New Caledonian region.

    Moving west to the Coral Sea and New Caledonian region including Vanuatu, we find a completely different looking regional form of P. ventralis. The males here differ primarily in their dorsal fin and tail coloration, as well as having a more reticulated spot pattern along the body just beneath the dorsal fin. The females are largely similar to those found in the type species. We will take a closer look as well as identify more clearly the differences below.

    [​IMG]Coral Sea Pseudanthias ventralis showing very consistently different coloration in males. Photo from Cairns Marine.

    In this region, the males are also steely purple in basal coloured, with the head encapsulated in yellow. The dorsum is also yellow washed, but contains a series of super imposed purple spots that conjoin to form a reticulated pattern travelling horizontally. In addition to that, a secondary set of yellow blotches and squiggles sit just beneath the purple reticulations. There are therefore two sets of body coloration here; a series of purple reticulated spotting on the yellow base of the dorsum, and a second set of yellow squiggles on the purple body coloration just beneath. The yellow squiggles is prominent enough such that it gives an impression of a separate line coming out of the head region and starting just behind the operculum.

    The dorsal fin takes on the reverse coloration as the type species, with the anterior spinuous portion coloured in yellow while the soft rays in red. The red coloration in the soft rays is only limited however to the anterodorsal region, and does not creep to the posteroventral base, where it is coloured yellow. This is delineated by a diagonal line originating from the purple spotting on the dorsum, which extends to the tip of the fin.

    [​IMG]Pseudanthias ventralis, male and female pair from the Coral Sea. Photo from BlueHarbor. Notice the difference in male patterning highlighted and arrowed in white.

    The caudal fin also differs by having a weak red blotch or bar near the edge, with purple lines along its margin which always fails to encircle it. Like the type species, the anal fins are clear, but has a strong purple line delimiting a more deeply colored region corresponding to the anal spines and first rays which form the elongate leading edge of the fin.

    Females are nearly identical to the type species with the same yellow dorsal fin and red arching stripe separating the two colours near the caudal peduncle.

    [​IMG]A closer look at the delimiting diagonal line on the dorsal fin as well as the double sets of reticulations on the body. Photos by SRS Vanuatu.

    The Vanuatuan specimens are identical in appearance to the Coral Sea specimens, and in the photo above, the delimiting purple line on the dorsal fin can be more clearly seen. The red anterodorsal region is separated clearly by the yellow posteroventral base of the dorsal fin by this purple line which may or may not originate from the purple spotting on the body. However this line is always present one way or another in this regional form.

    The photo above also more clearly demonstrates the purple spotting that can be seen here joining up into an irregular chain or reticulated pattern, very unlike the individual spots that pepper the type species in the Southern Pacific and French Polynesia. The secondary yellow squiggle that sits just beneath can also be observed.

    [​IMG]Males from New Caledonia. Photos by Tsumishima and Oceania.

    The New Caledonian forms are basically identical to those from the Coral Sea and Vanuatuan region. Seeing as they all sit within the same biogeographical area, it is unlikely that variations would be alarmingly vicariant. The New Caldonian forms however do appear to be slightly more erythric and richer in coloration, but it is unknown if this characteristic is from the fish itself or from camera settings in the photographs taken.

    The reticulated patterns on the dorsum do however appear to spread a little more extensively ventrally, but overall they do bear the same characteristics as the Coral Sea and Vanuatuan forms. The tail is also weakly spotted in red and the purple lines always fail to encircle it.

    Japan, Marianas and the Marshall Islands

    [​IMG]The Japanese and Marshall Island forms, with intermediates from the Marianas.

    Moving northwards from the Coral Sea, Vanuatu and New Caledonian region, a different complex of P. ventralis can be found. This quadrant comprise of individuals found in the Marshall and Mariana islands as well as Japan, where the species is at the western most limit of its range. The forms here are more variable than those in the preceding locales, and show a wide range of intermediates especially in the pattern on the caudal fin.

    [​IMG]Pseudanthias ventralis from Japan (Ogasawara). Photos A, B and C by Rising Moon, Plaza Rakuten and Masa Michishiro respectively

    The basal coloration of the males are as usual, steely purple with the head encapsulated in yellow. The dorsum is yellow washed as usual, and the purple spotting here are numerous, but small and never joined like the New Caledonian and Coral Sea forms. The specimens from this geographical area also lack the development of the secondary yellow squiggles found below the dorsum, and even if, it is usually highly vestigial and under developed.

    [​IMG]Pseudanthias ventralis from Saipan. Note the difference in male coloration highlighted in white. Photos A, B, C and D by Sealovers Saipan, Acetomatoe, Tadaki Wakasugi and Acetomatoe respectively.

    Dorsal fin is entirely orange or red sans the posterior soft portion which is always yellow. In this complex, there is an absence of a diagonal purple line delimiting the two colours on the fin. The most distinctive feature for this group is the highly developed red spotting on the caudal fin, which is present in all male specimens. In many cases the caudal blotch is almost fully circular, with varying completeness of encirclement from the bordering purple lines. In fact, it is not unusual to find specimens with a well developed caudal spot fully circumscribed by the bordering purple lines. Another distinctive feature for this group is the lack of any delimiting lines on the anal fin, being completely yellow.

    The males from this region have by far the most under developed dorsum markings, lacking the intricate reticulations that the other forms possess. They however are very unique in the caudal and anal fin characteristics, which is very much different from the other forms. The three photo collages from Ogasawara, Saipan and the Marshall Islands show some variability amongst individuals, especially in the development of the caudal blotch.

    However the specimens are consistent enough to warrant placement in the same biogeographical range, possibly belonging in the same complex.

    [​IMG]Pseudanthias ventralis from the Marshall Islands. Photos A, B, C by In-depth Kwajalein and D by SplashSea Japan.

    The females from this region are also different, and lack the distinctive red arching stripe that separates the yellow dorsum from the purple body. In most individuals, the stripe is entirely absent, or if rarely, found only as a thread.

    Philippines, Fiji and Palau (?)

    In our search, we’ve been unable to find any information or photos pertaining to this species’ existence in Fiji and Palau. Fiji sits in the middle of the Coral Sea and the Cook Islands, so it is not unlikely that the species can be found there as well. However if the absence of P. ventralis in Fiji is indeed certain, then it serves as a disjunct range between the Coral Sea individuals and those of the Cooks. This isolation could further support the speciation of the Coral Sea and New Caledonian forms.

    Its absence from Palau is also curious, being one of the Oceanic islands situated so close to Saipan and the Marshalls. Perhaps the lack of photos and information is due to it being exceedingly rare in the area, or perhaps it is totally absent there. Why or wether or not this is true, we are not sure.

    [​IMG]Pseudanthias ventralis from presumably Philippines. Aquarium specimen of Jacky Wong.

    P. ventralis can also be quite dubiously found in the Northern Philippines, where again it appears to be very rare. We’ve only managed to find a single photo of an aquarium specimen that arrived from a Philippine import. Being so close Japan, it is not unlikely that P. ventralis can be found there. The supposed Philippines individual above shares the same overall characteristics as the Japanese forms, and if anything it probably belongs in the same complex.

    Hawaii and Johnston Atoll

    [​IMG]The Hawaiian population of P. ventralis has speciated completely and has been awarded full taxonomic upgrade to P. hawaiiensis.

    The Hawaiian and Johnston Islands are home to a multitude of endemic species, one of which was a previous isolated form of Pseudanthias ventralis that has now attained full taxonomic upgrade. The fish, once known as a subspecies of P. ventralis, is now recognised as Pseudanthias hawaiiensis. P. hawaiiensis differs markedly from P. ventralis, with the basal coloration drifting away from the usual purple, to take on a rich burnt orange. The posterior third of the body fading toward the caudal peduncle is a light lilac. The purple spotting that is so characteristic of P. ventralis is reduced to a mere fraction in the males, and in some cases totally absent.

    [​IMG]P. hawaiiensis male. Photo from WetWebMedia.

    Interestingly, P. hawaiiensis also differs morphologically, with extremely long ventral fins; much longer than its sister species. These can often reach well pass the anal fins. The females, pictured below, is uniformly yellow, but in some individuals and perhaps under different lighting, the usual purple ventral portion of the body can be seen. Other than that, it is very much distinctive and different from the usual females of P. ventralis.

    [​IMG]Pseudanthias hawaiiensis female. Photo by Kevin Kohen.

     Table of comparison 

    [​IMG]A table of summary of Pseudanthias ventralis and its variations.

    Although this article is derivative and observational, but based on distribution as well as color variation, it is not unlikely that Pseudanthias ventralis houses more than one species in its complex. The Coral Sea and New Caledonian specimens seem highly likely to form a distinctive sister group, and more studies or examination should be done on those specimens.

    As far as fluidity in appearance goes, it seems that the males differ rather greatly from area to area, while the females remain relatively similar. The exception being those found in Japan, Marianas and the Marshall Is, where the females lack the red arching stripe that separates the yellow dorsum from its purple body. Males differ primarily in their dorsal and caudal fin markings, as well as the intensity and arrangement of the purple spotting on the dorum. In the New Caledonian and Coral Sea specimens, the spotting is not only highly conjoined and reticulated, but an additional set of yellow squiggles are present just beneath.

    P. hawaiiensis is a classic and very good example of allopatric speciation, where a new and totally distinct species has evolved away from the original lineage. It is entirely possible that some of these P. ventralis forms we’ve discussed today have begun speciating away from the original type, and further analysis may one day warrant the elevation of these variants to full species level.

    A big thank you to Joe Rowlett, who has been highly instrumental in the crafting of this article. The distribution maps as well as the coherence of this piece should be credited to him as well.
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