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Abrupt Change vs Moderate Graduality in a Transition Zone: From Herichthys cyanoguttatus to H. carpintis (The Search for the Missing Link)

By , 2005. printer
Published
Mauricio de la Maza Benignos, 1999

Classification: Distribution and conservation.

" Rio Grande (Bravo) and Soto la Marina drainage systems in northeastern México wihthold two different but closely related cichlid species, namely Herichthys cyanoguttatus and Herichthys carpintis. The distance between northern and southern affluents of these rivers is no more than 5 km. away, although a small geographical accident lays between them. This article explores how is the change in appearence between the two species, is there an abrupt or gradual change between them? How far how they radiated in evolutive terms? "

Border between Nuevo León and Tamaulipas
State limit between Nuevo León and Tamaulipas. Photo by Marco Arroyo.

It was Saturday, 6:30 A.M. and I was already "feeding gas" to "my mulita (little mule)", a tough little Nissan utilitarian truck that when not at work serves as an all-terrain on my expeditions across the country. Cast nets, hand nets, masks, snorkels, etc. set and ready to pick my friend Marco Arroyo, and depart South from Monterrey on our quest across two major basins of North-eastern México: the Conchos or San Fernando, and the Soto La Marina across their Western most areas and tributaries.

Our main goals were to (1) verify the authenticity of certain reports -including some rather old ones and a rather recent one of mine- of H. cyanoguttatus along the Soto La Marina basin, and (2) to determine the Western-most distribution of the large, horizontal-row doted H. cyanoguttatus that appeared in the Cichlid Room Companion forum, and that was identified by Juan Miguel Artigas Azas as "The Herichthys cyanoguttatus... from Rio Conchos (San Fernando). Its distinguishing feature is the horizontal rows of larger dots (larger than in H. cyanoguttatus from Rio Bravo)." (CRC, Cichlid Room Forum, Central American Cichlids, Herichthys cyanoguttatus, July, 12th, 2005).

As we departed South through the National Highway 85, and much to our disappointment, Marco and I began to notice how the rivers and normally dry streams of the San Juan basin (just north of the San Fernando), were carrying muddy water (remnants of Hurricane Emily) from the Sierra Madre ridge at which base we were driving. Nevertheless, we managed to keep our spirits high and kept going.

The first stop, state limit between Tamaulipas and Nuevo León

While "en-route" we were rewarded with the sight of clearer (but still turbid) waters draining from the impressive mountains, standing tall, proud and green of the Sierra Madre, in contrast to the semi-arid landscape of southern Nuevo Leon, which is broken only by the irrigated orchards of México's Northeastern citrus belt.

We were in the municipality of Montemorelos, world known by its sweet and juicy oranges, which are irrigated with the waters of the upper San Fernando basin. The rivers were still grown, but the waters were already clearer in such latitudes.

Since we were on a tight schedule, Marco and I decided to move forward to the very point where the states of Nuevo Leon and Tamaulipas are divided by what the maps show as an intermittent stream, but that always carries enough water to maintain a small, but interesting population of cichlids year round in some of its pools.

State limit between Nuevo León and Tamaulipas

Creek in the State limits of Nuevo León and Tamaulipas
Creek in the State limits of Nuevo León and Tamaulipas. San Fernando Basin, Conchos, habitat of Herichthys cyanogutattus. Photo by Marco Arroyo.

This particular place was central to our objectives for the following reasons: (1) it is the southernmost secondary tributary within cichlid-range-altitude of the upper San Fernando (Conchos) basin. (2) It runs only 5 km (less than 3 miles, and a 5 minutes drive) north of the northernmost first major tributary of the Soto La Marina basin, the Río Magueyes. (3) While the Soto La Marina basin and the San Fernando basin are separated by topographical accidents like the San Carlos Ridge and the Chiquita ridge, the topography of the 5 km stretch which belongs to the Sierra Chiquita at that particular point is almost imperceptible to the visitor.

A large-horizontally-dotted Herichthys cyanoguttaus can be found in the San Fernando basin, Conchos.

For the above reasons, Marco and I decided to park the truck, to descend down the creek, and to do a little bit of scouting up and down the stream, around the bridge that crosses it. The normally transparent waters were still a little bit turbid. The current was flowing stronger than usual. Sand had been deposited in what used to be the deeper banks of the creek, and the current had dug deep in the shallow sections. The vegetation on the sides was still laying, proof of the recent flooding, and a few rather small mollies (Poecilia mexicana) were hanging around, but there were no visible signs of other forms of animal life.

At that point, we decided to fetch the nets, and to do a last hike up river. As we were struggling against the fast flowing waters of the normally calmed stream, we noticed a calmer section. We moved towards it, and as we stepped in, a school of juvenile Herichthys type cichlids rapidly swam to cover underneath the root-invaded "cave" that had been dug by the recent floods. Immediately, we grabbed the hand nets, and spent the next hour and a half unsuccessfully trying to catch one or two of our elusive friends.

We tried it all! At that point we decided that it was time to disturb the waters, to bet it all, and to prove our luck at the risk of eliminating the little visibility that was left in the pool. We began throwing some blind casts with the cast-net……. Five casts later, and a slip that had me sitting on the rocky bed searching for my glasses…… and there we had them: A most beautiful pair in early breeding coloration with large horizontal dots, of the type that was placed in the forum of the CRC.

The first conclusion of the day: A large-horizontally-dotted-Texas-Cichlid, Herichthys cyanoguttaus spp. San Fernando similar to the one reported by Artigas in the lower Conchos (Artigas, Juan Miguel, personal communication) can be found in the Western-most up-river affluent of the same basin too. From this it could be reasonably hypothesized that such cichlid inhabits the entire basin, an excellent excuse to investigate and to do another trip.

At this point, Marco decided that he would keep and try to breed at home the specimens that had been collected. So, after bagging them, and placing them in an icebox, we left for our next destiny: Río Magueyes (tributary of Río Pilón, not to be confused with Río El Pilón of the San Juan basin), which is the northern most tributary of the upper Soto La Marina basin, and home to the elusive, rarely seen and mysterious pitviper Cantil Tamaulipeca (Tamaulipas moccasin), Agkistrodon taylori.

The Territory of Herichthys carpintis teporatus, The Magueyes River

Rio Magueyes, Soto la Marina
Rio Magueyes, Soto la Marina; habitat of Herichthys carpintis. Photo by Marco Arroyo.

Again we decided to move down a partially destroyed dirt road, to park "the mulita" and to descend nets in hand down the muddy banks to the beautiful, this time blue-clear waters of the Río Maguelles. It soon became evident that the river had grown here too, as our feet sank above the ankles in the mud. It was at this point that Marco lost one of his slippers, and "bit the dust" evening-out the score one to one in terms of visits to the ground. Also, it is yet not clear to me if I am attracted to snakes, or snakes are attracted to me, or maybe the recent floods and the heat/humidity were to blame, but from that point on, the sight of such intriguing creatures accompanied us for the rest of the journey, at times distracting my attention from the cichlids, and creating an unwelcome state of anxiety in Marco, whom, in his own words "is not very fond of the reptiles".

Marco was amazed at the abruptness in terms of species change from one location to the other, we had barely left 5 kilometres behind.

In sight of the potential difficulties for reaching the river, Marco and I had decided to take with us only the indispensable gear (cast nets, bags and rubber bands). At this particular point, it became rather easy to net some cichlids out, so we took some samples: clearly Herichthys carpintis. We also saw some pairs in breeding coloration, but no fry. We assumed that the floods probably had taken the fry from them. As expected, there were no extraordinary findings. Marco was amazed at the abruptness in terms of species change from one location to the other. We had barely left 5 kilometres behind.

After less than an hour we managed to return to the truck with a bucket full of water to rinse our muddy feet, we packed our gear including three specimens of H. carpintis, and left for a new destination: Barretal, the place where I had collected and released the previous year some specimens of what I though were juvenile H. cyanoguttatus.

El Barretal

Rio Barretal

Herichthys carpintis (left), Fundulus grandis (Gulf killifish) (right) from Rio Barretal, Soto la Marina. Photos by Marco Arroyo.

Barretal is a small town crossed by the main highway, and irrigated by the San Antonio river, which in turn is formed by smaller tributaries including the Purificación river which begins in Aramberri valley, in the highlands of the neighboring state of Nuevo León (Soto La Marina drainage). The moderate sized river runs modestly throughout most of the year within a rather wide river-bed. This means that the river can grow wide and large during the rainy season. At the time, and at this point the river was a little bit grown, running with clear water, and with a rather strong current, which made it difficult to swim and snorkel in it.

In the light of the above, Marco and I decided again to cast the nets for a while, and see what happened. Some of the fish collected were: Poecilia mexicana limantouri (Mexican molly); Poecilia formosa (Amazon molly); Gambusia sp. and Fundulus grandis (Gulf Killifish). Regarding cichlids, the introduced Oreochromhis sp. was collected as well as Herichthys carpintis. No H. cyanoguttatus or anything that resembled it was collected or seen.

Río Corona

In the Corona River we were able to collect and see some of the most beautiful specimens of H. carpintis of the upper Soto La Marina.

Our next stop was the Corona River. The Corona River is the southernmost tributary of the upper Soto La Marina basin. Here we were able to collect and see some of the most beautiful specimens of H. carpintis of the upper Soto La Marina. It is at this point where last year I collected an alfa-male of magnificent colours which unfortunately did not make it home. Unlike the previous rivers, the Corona is a highly covered and shadowed river, it is vegetated, and it has a rather slow flowing current and even some tanine tainted areas with a sandy bottom rich in organic material from the leaves that fall to the water from the surrounding trees.

It is here that we were able to collect some juvenile specimens of extraordinary colours, as expected, together with more mollies, gambusias, the ever present Astyanax mexicanus and some colorful specimens of the locally very abundant crustacean Procambarus clarkii.

Rio Corona

Herichthys carpintis from Rio Corona, Soto la Marina. Photos by Marco Arroyo.

The River Without a Name (Josefina´s)

At 5:00 P.M. we were back in the truck, packed and ready to move to our next and final destination. A river which name no one seems to know, a tributary of the same San Antonio river that runs through Barretal, in the Soto la Marina drainage.

At El Tomaseño, we took a left, crossed the town of Hidalgo, and entered a micro climate with an ecosystem that reminds more of tropical Veracruz and Tabasco than the arid lands of Northeastern México. Here at the foot of the Sierra Madre, one may see Papaya trees growing wild, as well as an occasional Banana plant growing in the backyard of still present hay-roofed-adobe-huts. In the skies one may see an occasional peregrine falcon (Falco peregrinus) or a fishing osprey (Pandion haliaetus) soaring the skies, and looking for fish amongst the maze of irrigation canals and dams that cut the whole area into fragments like a puzzle.

It is here that one may see an occasional school of sword-tailed-platys (Xiphophorus xiphidium) swimming in some of the heavily vegetated ditches. These flow from cool water springs into the rivers that form the Soto La Marina basin.

At 6:30 P.M. we arrived to the river that runs through Ejido La Independencia. Here no one knew the name of the river, and some even informed us that "the river had no name". It was only a small boy whom we asked that told us that the name of the river is "Río de Josefina" (Josefina´s river). The above was done -according to him- in honour of the oldest lady in town who lived just by the river bank, and who scared kids away as they tried to go for a swim. Unfortunately they had to pass through her back-yard in order to do so.

It is in this river that Marco and I were astonished by the large number of cichlids in breeding dress, chasing each other in a clear and shallow pool (about 50 m long by 15 m wide and 1 m deep) formed by some man-piled stones placed across the river. Some of the fish looked somehow different from the ones that we had collected in the previous rivers. We decided to immediately cast the net.

Rio Josefina

Herichthys carpintis dot salad at Rio Josefina(?), Soto la Marina. Photos by Marco Arroyo.

The last hour findings

It was the first cast that really caught our attention. Cichlids were so abundant that it became almost impossible not to pull out the net without at least three specimens per cast. While I released the fish from the cast-net, Marco would pick them off the ground and place them into the stone-aired bucket. I was too concentrated untangling a stuck Poecilia mexicana from the net, when I heard Marco say: "It's cyanoguttatum!!!"

Immediately, I left what I was doing, and looked down to see the fish. We had caught what appeared to be a dot-less grey-based Herichthys type, and a horizontally aligned small dotted Herichthys that reminded us of the H. cyanoguttatus from the Conchos basin. We took photographs of them, decided not to jump into conclusions, and went on collecting.

As we advanced, and collected a larger sample (20 +), it became evident that this population was extremely variable in comparison to what had been previously seen in the other rivers. (a) In terms of base colour it went from solid green to grey. (b) In terms of dots it went from almost no-dots to abundant large dots, (c) in terms of dot colour, it went from aqua-green to sky blue, (d) in terms of dot alignment it went from horizontally aligned to randomly patterned, (e) in terms of dot shape it went from scaly to circular, and (f) in terms of body shape, males went from the typical nuchal humped H. carpintis shape, to a more moderate, less humped H. cyanoguttatus shape.

It was becoming late and the sun was setting behind the mountains. We had less than an hour to snorkel, bag the fish, pack our gear and start driving all the way back to Monterrey.

We were able to see: Dionda sp. some very beautiful Xiphophorus xiphidium, Poecilia mexicana limantouri and Astyanax mexicanus. A fisherman that passed nearby was carrying Ictalurus sp. and Micropterus salmoides. At 9:00 P.M., we decided to move on. At 3:00 A.M. we were back at Marco's place setting the last fish in his nice fish room.

A closer analysis

The next day, Marco and I met at his place. A closer analysis and a good light revealed that the specimens from "Ejido Independencia" (last collecting sport) were clearly H. carpintis, with a high degree of variability in terms of colour and shapes An estimated 10 percent presenting a solid phase, resembling its northern neighbour H. cyanoguttatus to a degree that, had they been collected in a H. cyanoguttatus locality, they would have passed as such. No wonder that collectors in the area -including myself- have been fooled!!!

Is this proof of the evolutionary break that took place in that area after the last glaciation, that split an ancestral and pseudo-extinct cichlid into modern H. cyanoguttatus and H. carpintis? Or, could it be that a population of H. cyanoguttatus may have been relatively recently introduced in the area, as forage for bass in the artificial lakes up-river and around; and that such population hybridized with the native H. carpintis? Or, is it possible that Del Villar (1970) is correct when considering both populations a single species with three different sub-species: H. cyanoguttatus cyanoguttatus, H. cyanoguttatus teporatus and H. cyanoguttatus carpintis?

Conclusions

Herichthys cyanoguttatus and H. carpintis do not live sympatrically in the Soto La Marina basin.
  1. In terms of colour there seems to be two dominating well marked dotted phases of H. carpintis (teporatus) through-out the upper Soto La Marina basin, and a less common localized almost solid phase -that could easily be confused with H. cyanoguttatus- in some areas of the San Antonio River (including Barretal)
  2. .
  3. While the change in terms of species from the San Fernando basin to the Soto La Marina basin is well marked and abrupt, there seems to be a gradual, but well marked change in terms of general appearance, colour, markings pattern and shape in populations between the Northern San Juan basin that drains to the Rio Grande; the San Fernando/Conchos basin that drains directly to the Gulf of México (At the mouth of Rio Grande); and the Soto La Marina basin that also drains directly to the sea. The above in contrasts to the more subtle changes that appear in the more northern range (Rio Bravo (Grande) Drainage) of H. cyanoguttatus.
  4. H. cyanoguttatus and H. carpintis do not live sympatrically in the Soto La Marina basin. However, some localized members of the Soto La Marina population resemble the H. cyanoguttatus from the San Fernando basin. Since mixed pairs -solid and dotted phases- were observed, it becomes clear that all phases interbreed and ensue, it may be concluded that:
    1. If such variability reflects the recent introduction of H. cyanoguttatus into the basin, such genes are being rapidly absorbed into the main population, and the "cyanoguttatus" phenotype should disappear with time.
    2. On the other hand, such variability may reflect the tremendous genetic potential that characterizes cichlids, and the consequent capacity of adaptation and change that has allowed Herichthys to radiate and become dominant in the Neoarctic Northeastern México.

References

Citation

de la Maza Benignos, Mauricio. (August 03, 2005). "Abrupt Change vs Moderate Graduality in a Transition Zone: From Herichthys cyanoguttatus to H. carpintis (The Search for the Missing Link)". Cichlid Room Companion. Retrieved on December 16, 2018, from: https://www.cichlidae.com/article.php?id=357.