ena-STUDY-UNIVERSITY OF KONSTANZ-18-06-2018-18:17:12:397-5952
Lessons  from  a  natural  experiment:  Allopatric  morphological  divergence  and  sympatric  diversification  in  the  Midas  cichlid  species  complex  are  largely  influenced  by  ecology  in  a  deterministic  way
Explaining  why  some  lineages  diversify  while  others  do  not  and  how  are  key  objectives  in  evolutionary  biology.  Young  radiations  of  closely  related  species  derived  from  the  same  source  population  provide  an  excellent  opportunity  to  disentangle  the  relative  contributions  of  possible  drivers  of  diversification.  In  these  settings,  lineage-specific  effects  are  shared  and  can  be  ruled  out.  Moreover,  the  relevant  demographic  and  ecological  parameters  can  be  estimated  accurately.  Midas  cichlid  fish  in  Nicaragua  have  repeatedly  colonized  several  crater  lakes,  diverged  from  the  same  source  populations,  and,  interestingly,  diversified  in  some  of  them  but  not  others.  Here,  using  the  most  comprehensive  molecular  and  geometric  morphometric  data  set  on  Midas  cichlids  to  date  (~20,000  SNPs,  twelve  landmarks,  ~700  individuals),  we  aim  to  understand  why  and  how  crater  lake  populations  diverge  and  why  some  of  them  are  more  prone  to  diversify  in  sympatry  than  others.  Taking  ancestor-descendant  relationships  into  account,  we  find  that  Midas  cichlids  diverged  in  parallel  from  their  source  population  mostly  -  but  not  exclusively  -  by  evolving  more  slender  body  shapes  in  all  six  investigated  crater  lakes.  Admixture  among  crater  lakes  has  possibly  facilitated  this  process  in  one  case,  but  overall,  admixture  and  secondary  waves  of  colonization  cannot  predict  morphological  divergence  and  intralacustrine  diversification.  Instead,  morphological  divergence  is  larger  the  more  dissimilar  a  crater  lake  is  compared  to  the  source  lake  and  happens  rapidly  after  colonization  followed  by  a  slow-down  with  time.  Our  data  also  provide  some  evidence  that  founder  effects  may  positively  contribute  to  divergence.  The  depth  of  a  crater  lake  is  positively  associated  with  variation  in  body  shapes  (and  number  of  species),  presumably  by  providing  more  ecological  opportunities.  In  conclusion,  we  find  that  parallel  morphological  divergence  in  allopatry  and  the  propensity  for  diversification  in  sympatry  across  the entire  Midas  cichlid  fish  radiation  is  partly  predictable  and  mostly  driven  by  ecology.
Explaining  why  some  lineages  diversify  while  others  do  not  and  how  are  key  objectives  in  evolutionary  biology.  Young  radiations  of  closely  related  species  derived  from  the  same  source  population  provide  an  excellent  opportunity  to  disentangle  the  relative  contributions  of  possible  drivers  of  diversification.  In  these  settings,  lineage-specific  effects  are  shared  and  can  be  ruled  out.  Moreover,  the  relevant  demographic  and  ecological  parameters  can  be  estimated  accurately.  Midas  cichlid  fish  in  Nicaragua  have  repeatedly  colonized  several  crater  lakes,  diverged  from  the  same  source  populations,  and,  interestingly,  diversified  in  some  of  them  but  not  others.  Here,  using  the  most  comprehensive  molecular  and  geometric  morphometric  data  set  on  Midas  cichlids  to  date  (~20,000  SNPs,  twelve  landmarks,  ~700  individuals),  we  aim  to  understand  why  and  how  crater  lake  populations  diverge  and  why  some  of  them  are  more  prone  to  diversify  in  sympatry  than  others.  Taking  ancestor-descendant  relationships  into  account,  we  find  that  Midas  cichlids  diverged  in  parallel  from  their  source  population  mostly  -  but  not  exclusively  -  by  evolving  more  slender  body  shapes  in  all  six  investigated  crater  lakes.  Admixture  among  crater  lakes  has  possibly  facilitated  this  process  in  one  case,  but  overall,  admixture  and  secondary  waves  of  colonization  cannot  predict  morphological  divergence  and  intralacustrine  diversification.  Instead,  morphological  divergence  is  larger  the  more  dissimilar  a  crater  lake  is  compared  to  the  source  lake  and  happens  rapidly  after  colonization  followed  by  a  slow-down  with  time.  Our  data  also  provide  some  evidence  that  founder  effects  may  positively  contribute  to  divergence.  The  depth  of  a  crater  lake  is  positively  associated  with  variation  in  body  shapes  (and  number  of  species),  presumably  by  providing  more  ecological  opportunities.  In  conclusion,  we  find  that  parallel  morphological  divergence  in  allopatry  and  the  propensity  for  diversification  in  sympatry  across  the entire  Midas  cichlid  fish  radiation  is  partly  predictable  and  mostly  driven  by  ecology.