Yumurta qoymaqdan doğum etməyə keçid edən növ qeydə alınıb

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Elm adamları, Avstraliya kərtənkələ növünə aid bir sürünənin yumurta qoymaqdan uzaqlaşıb niyə doğum etməyi seçim etdiyinin şifrələrini həll etdi.


New South Wales’in isti sahil düzənlikləri boyunca, sarı qarınlı, üç barmaqlı qum kərtənkələləri, çoxalmaq üçün yumurtalarını buraxırlar. Ancaq, daha yüksəklərdə və soyuq dağlarda yaşayan eyni növə aid fərdlər, nəsillərini davam etdirmək üçün doğum edirlər. National Geographic’də iştirak edən xəbərə görə, yalnız bunun xaricində iki müasir dövrün sürünəni, – başqa bir qum Kərtənkələsi növü və Avropa kərtənkələsi- iki cür çoxala bilir. Təkamül qeydləri, yüz sürünən soyun keçmişdə yumurta qoymaqdan doğum etməyə keçid etdiyini göstərir. İndiki vaxtda isə ilan və kərtənkələlərin təxminən 20%i doğum edirlər.

East Tennessee State Universitetindən olan araşdırmanın müəlliflərindən James Stewart, müasir dövrün sürünənlərinin balalarının uzun bir təkamül zaman içində anlıq bir poza olaraq qarşılarına çıxdığı halda, sarı qarınlı-üç barmaqlı qum kərtənkələsinin bu ikili davranışı bu səbəblə elm insanlarına nadir bir araşdırma sahəsi təqdim etdiyini deyir.  Prosesin fərqli mərhələlərində  fərqlilikləri araşdıraraq, bir artıma davranışından digərinə keçidin nəyə bənzədiyini ortaya qoya bilərsiniz.

Yumurtlamaqdan doğuma keçid qida sıxıntısı yaradır

Sürünənlər yumurtaqoymaqdan bala doğumu keçişindəki ən böyük sirrlərindən biri, doğumdan əvvəl körpənin necə bəsləndiyidir. Məməlilərdə, plasentanın əsas vəzifəsi, inkişaf etməkdə olan dölün ehtiyac duyduğu qida maddələrini anadan körpəyə köçürmək, dölün maddələr mübadiləsi nəticəsində çıxardığı tullantı məhsulları ananın dövranına köçürmək və yenə ana ilə körpə arasında oksigen və karbondioksid mübadiləsini təmin etməkdir.

Yumura qoyan növlərdə isə, embrion, qidanı yumurtanın sarısından almaqla bərabər, məsaməli qabıqdan əmilən kalsium da onlar üçün əhəmiyyətli bir qida qaynağıdır. Bəzi balıq və sürünənlər iki doğum növünü də istifadə edir. Ana yumurtaları meydana gətirər ancaq rüşeym inkişafın son mərhələlərinə qədər bədəni içində onları qoruyur. Bu adaptasiya prosesi potensial bir qida problemi yaradır. İncə qabıq az kalsiuma malikdir və bala sürünənlərdə qida çatışmazlıqlarına səbəb ola bilər.

Qum kərtənkələləri haqqında illərcə çalışan Stewart və qrup yoldaşları, sarı qarınlı üç barmaqlı qum kərtənkələsinin rəhm quruluşu və kimyasına baxaraq qida problemi haqqında ipucları tapmağa çalışdılar. Stewart, “İndi görürük ki rəhm kalsium yaradaraq embriona qatılır. Bu sadəcə sürünənlərdəki plasenta təkamülünün erkən dövrlərində mövcuddur”deyərək gəldikləri nəticəni açıqlayır.

Təkamül keçidi çaşdırıcı dərəcədə sadədir

Hər iki çoxalma növündə də təkamül söz mövzusudur. Yumurtalar xarici təhdidlərə və qeyri-adi hava şərtlərinə qarşı müdafiəsizdir. Rahim içində isə anaya daha çox yük düşür. Qum kərtənkələnin üçün, isti iqlimlərdə inkişafın son həftəsində ana yumurtaların üzərinə yataraq qorumağı tərcih etdiyi halda, sərt iqlimlərdə yaşayan ana isə, tam tərsinə balalarını qorumaq üçün bədəninin içində uzun müddət saxlamağı seçim edir.

Stewart, “Araşdırma nəticələrinə görə, ümumi olaraq sürünənlərdə yumurtaqoymaqdan, doğum etməyə keçid olduqca məşhurdur, çünki nisbi olaraq keçid etmək olduqca sadədir” deyir. “Ümumi olaraq keçidin çox kompleks olduğunu düşünürük, lakin bəzi hadisələr düşündüyümüzdən daha sadə görünür.”

Qum kərtənkələlərinin təkamülü  Morpohology jurnalında nümayiş olunub.

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